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Keewech Laboratory 

Compiled by Barrington S. Havens 

Public Relations Services Division 

Report No. RL-756 July 1952 






Available to anyone upon request. 

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| in T. I. S. Briefs. 

Available to G-E employees for use within 
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Rigidly limited distribution within the Company. 
May not be sent outside the United States. 

(Class 4 reports should be returned to Research 
Laboratory Publications if they are not needed.) 

Kecewuk Libovalty 



Compiled by Barrington 8. Havens 
Public Relations Services Division 

July 1952 

Published by 
Research Publication Services 
The Knolls 
Schenectady, New York 


Reseach Labowliy 



Title Page 
Havens, RL-756 
Barrington S. meteorology July 1952 
TITLE Tapes ae 
History of Project Cirrus 

Project Cirrus, initiated on February 28, 1947 under 
Contract W-36-039-sc-32427, requisition EDG 21190, was 
established to cover ‘‘research study of cloud particles an 
cloud modifications.’’ Project Cirrus continued through th 
life of several government contracts, ending in 1952. A 
history of the project covers not only the work done under 
ae Seen Lae Research Publication 

; Services 105 
BSNCLUSIGNS° Sq o> sag Tai. Sk ee ee 
history of the project covers not only the work done under 
government contract but also the work of General Electric 
scientists for many years leading up to the establishment 
of the project. 

By cutting out this rectangle and folding on the center line, the above information can be fitted 
into a standard card file. 





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Pineapple Research Institute, Honolulu, Hawaii...... 
Milliken & Farwell, Mobile, Alabama............... 
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Modifying Stratiform CloudS..........-.++.sse+ee- 
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Bibliography of Reference Literature ......... 



This history of Project Cirrus was prepared at the request of the 
Research Laboratory for three reasons. First of all, the project has been-- 
and still is, at this writing--of such unusual interest and significance, that 
the telling of the story is merited for its own sake. Secondly, the termina- 
tion of the project is bound to result in an eventual dispersal of the various 
members of its personnel. Already Dr. Langmuir has retired from active 
General Electric employ, and the other members of the project are, and 
will be, more and more engaged in new and completely different activities. 
And finally, the broad aspects of the project have such wide implications that 
it is particularly important that the story be committed to paper ‘for the 

It has not been easy to organize the raw material in any simple, logical 
fashion. As is so often the case, the project was very complex, with a num- 
ber of subdivisions associated with the main activity. Some of these subdi- 
visions ran consecutively, some operated in parallel, and others intertwined 
or branched off in variously divergent directions. 

Where it was possible the material has been arranged in chronological 
or otherwise logical order. Where it was not possible, the various subor- 
dinate topics have been taken up in as nearly a logical order as possible. As 
a result, cases will be found where the story “‘gets ahead of itself”’, and 
later it becomes necessary to retrace one’s steps to pick up the thread. 

The history, with the exception of the Introduction and Conclusion, 
divides itself naturally into two main parts. The first is the story of the 
early activities which led to the formation of Project Cirrus. The second 
is the story of Project Cirrus itself. 

Schenectady, New York — B.S. Havens 
July, 1952 


It would be difficult, if not impossible, to trace the complete lineage 
of everything leading up to Project Cirrus. General Electric scientists were 
not the only ones who studied many of the problems involved. And even when 
restricting consideration to General Electric research projects, the situa- 
tion is complicated. 

The following material is confined as much as possible to work which 
has a relatively direct bearing on Project Cirrus research. 


The earliest activity leading directly to Project Cirrus was the study, 
beginning in 1940, of the fundamental nature of filtration in gas masks. This 
work was undertaken by Dr. Irving Langmuir ens Dr. Vincent J. Schaefer at 
the request of the Chemical Warfare Service. 12) 

‘Gas masks normally use charcoal to absorb poison gases, but even in 
World War I the possibility arose that the enemy might use toxic smokes 
which could not be absorbed by charcoal and thus would have to be removed 
by.a filter somewhat like filter paper. 

The first step in attacking the problem was to make some smokes of 
the type for which the filters would be used. In doing so, the scientists stud- 
ied the particles which composed the smokes. They investigated such things 
as particle stability, concentration, and measurement. They obtained fairly 
successful theoretical results and a better understanding of how to build a 
good filter. And incidentally, they acquired a great deat of detailed know- 
ledge as to how to make a smoke which would be non-volatile and would con- 
sist of particles far smaller than those of ordinary smokes, and they learned 
much about optical properties. 

This work was done under a National Defense Research Committee 
contract. As Langmuir and Schaefer neared the end of the work, a form 
letter was received in August, 1941, asking if anyone could think of a way 
to make a white screening smoke that could be used over large areas to 
cut down the hazard from aerial bombardment. 

Langmuir and Schaefer wondered whether they couldn’t do this by 
using the methods they had adopted for making smokes for testing filters. 

They decided to try. 

They had found that the easiest way to make smokes and control the 
particle size was to take some oil and put it into a volatile condition. They 

Early History -4- 

heated oleic acid and similar substances up to about 200°C and passed a 
stream of air over them to get the vapor mixed with air. Then they quenched 
the mixture suddenly by blowing in a large amount of cold’ air. The parti-> 
cles grew in size and by sudden quenching they found they could stop the 
growth at any desired point and also make particles of very small size. 
They were surprised to find that, under certain conditions, they could get 
particles of extraordinarily uniform size. 

Further work and experimentation showed thatthey could do the same 
thing on a large scale. Larger generators were built, tests were made, and 
the design was adopted by the Army and used successfully and on a large 
scale curing the war. : 


Quite independently of this work the Secretary of War asked in 1948 
for research into the problems of precipitation static.(12) It was believed 
that the invasion by Japan would have to come very largely from air attacks 
through the Aleutian Islands, across Alaska, and from the North. That led to 
a tremendous development of air transport and airplanes through the Aleutians. 

The difficulty in flying aircraft in the Aleutians was very serious. One 
of the big problems was icing of the aircraft, but even more baffling was the 
complete loss of radio contact when the planes flew through snowstorms. The 
planes might become charged, sometimes, to a potential of 250,000 volts or 
more, producing corona discharges from all parts of the plane and causing such 
electrical disturbances that radio sets could not receive messages. Pilots had 
particular difficulty in finding their bases and getting down through this foggy 
bad weather. What could be done about it? 

Langmuir and Schaefer were interested. They had no particular ideas 
on the subject, except that it had to do with weather. In their opinion, the best 
place to investigate something like that was the well-equipped laboratory of the 
Mt. Washington Observatory on top of Mount Washington in New Hampshire. 

Mount Washington in winter has an average temperature of minus four 
or five degrees F, the wind averages about 60 miles per hour, and most of the 
time clouds sweep over the summit. It seemed to offer the proper conditions - 
for a research of this kind. 

So equipment was installed at the summit, and Schaefer went there. sev- 
eral times during the winter of 1943 to conduct experiments. But he discov- 
ered that anything exposed there during the winter immediately became cov- 
ered with ice, because the air was full of supercooled water droplets. He and 
Langmuir became So much interested in this that they hoped they would not 
have to continue a long study of precipitation static. 

Early History aie 

In the course of this work, Schaefer relied heavily on the services 
of Raymond E. Falconer, who was then one of the observers in the weather 
station on the summit. 


It So happened that the Army Air Forces were just as much interested 
in problems of aircraft icing as in precipitation static. This fitted in so well 
with the new interest of ae and Schaefer that in 1944 they starteda 
study of icing of aircraft. 32A) 

They had much assistance from Victor Clark, Falconer, and others 
of the observatory personnel, who were already working on riming and 
icing. Langmuir and Schaefer, however, were able to introduce Some new 
and very productive ideas. 

Extensive mathematical calculations were necessary. The first work 
of this nature was done by Langmuir, and his results were used in connec- 
tion with the cloud studies at Mount Washington (see below). During the 
later stages of the Mount Washington studies, Langmuir decided to make use 
of a differential analyzer for these calculations, and in preparing the mat- 
erial for that purpose, he was assisted by Dr. Katharine Blodgett. Thus 
it was possible to calculate the percentage of water droplets which would 
be depesited on a given surface under specific conditions, The information 
was used on data obtained on Mount Washington to determine the number 
and size of water droplets involved in the formation of ice. 


The theoretical calculations worked beautifully in practice. They 
began to acquire a very satisfactory understanding of some features of 
cloud structure and the growth of cloud particles. They became absorbed 
in this new interest. And Langmuir found he could apply to his smoke gen- 
erator work the same evaporation-condensation theory he had used to cal- 
culate the growth of smoke particles. 

But, although they felt they had a fundamental theory for some of the 
factors that caused particles to grow in clouds to the size they are, they 
didn’t feel conditions were right for further study on Mount Washington. 
It would be far better to study cloud particle growth in airplane flights. 
That would require the development of new instruments. 

This was late in 1946. They took the question up with the Army Air 
Force and the Signal Corps. They were led to think that perhaps some- 
body might furnish aircraft for experimental purposes of this sort; it 
seemed that it would be desirable to know something about clouds from a 

Early History -6- 

standpoint of national defense. But they didn’t get along very fast. They 
carried the research along on their own to a large extent, testing instruments 
on Mount Washington, but they never got tests in aircraft. 


By this time they were deeply interested in their cloud study. They 
investigated and learned a lot of things. But the thing that struck them most 
was that, if there are any snow crystals in a supercooled cloud, they must 
grow rapidly and should tend to fall out. They came to the conclusion that 
in winter, if there are supercooled stratus clouds from which no snow is 
falling, even though the temperatures in the clouds are below freezing, there 
simply are no appreciable numbers of effective snow nuclei. Such clouds can 
apparently be supercooled to very low temperatures. 

They thought this presented a problem that should be investigated. Why 
was it that sometimes snow forms so easily, with apparently no lack of nuclei 
on which crystals can grow, and at other times there seem to be none? They 
concluded there must be something in the atmosphere that causes water drop- 
lets to change to ice only at certain times and under various conditions. They 
decided to make some careful experiments in the laboratory in an attempt to 
duplicate those conditions. 


During Langmuir’s absence in California for three or four months in 1946, | 
Schaefer made what Langmuir has described as ‘‘some beautiful experiments? (1! 
During the previous winter he had been studying the behavior of droplets on cold 
surfaces to see how they supercooled or froze as the temperature dropped. He 
had found he could supercool water drops to as low as -20°C on surfaces coated 
with polystyrene and similar materials. He had realized, however, that such 
experiments were not simulating supercooled clouds and had sought a better 
method of experiment. 

He decided to try a home freezing unit of the type used for food storage. 

He lined it with black velvet so he could get a good view of what happened inside 
when he directed a beam of light down into the box. He then breathed into the box, 
and the moisture condensed and formed fog particles which were just like ordin- 
ary cloud particles, although the temperature was about -23°C. No ice crystals 
formed. He tried many different substances dusted into the box to get ice crys- 
tals to form, but almost never got any. He got just enough to convince him that, 
if he did get them he could easily see them. 

Finally, one July day when the temperature of the chamber was not low 
enough, he put a big piece of dry ice into it to lower thetemperature. In an 
instant the air was full of ice crystals. The crystals persisted for a while 

Early History ae 

after he took the dry ice out. 

Following this discovery, Schaefer conducted a number of experiments. 
These showed that even a tiny grain of dry ice would transform the super- 
cooled cloud in the cold box to ice crystals. Quantitative experiments were 
conducted which showed that many millions of crystals could be produced 
in this manner. 

In order to find out if there was something peculiar to dry ice which 
produced this effect, he worked with other cold materials. For example, 
he showed that, by dipping a common sewing needle into liquid air and then 
passing it momentarily through the supercooled cloud in the cold box, sim- 
ilar spectacular effects occurred. This demonstrated that the presence of 
a sufficiently cold substance was all that was required to produce the effect. 
Schaefer devised methods and equipment for determining, with considerable 
accuracy, the fone temperature at which the supercooled cloud changed 
to ice crystals. 36) This temperature was found to be -38.9C+0.1 degree. 

Schaefer’s discovery changed the whole situation. It meant, first, that 
it was not the dry ice or the needle as such that was responsible for the ef- 
fect, but the temperature. Anything could be used having a temperature of 
-40-C or colder. 


Meanwhile the stage had been set for another important contribution 
to this pioneering work in meteorology. Before Dr. Bernard Vonnegut be- 
came associated with the General Electric Research Laboratory, he was 
employed at Massachusetts Institute of Technology, where he had been en- 
gaged in various stwiies during the early years of World War II, In the 
laboratory of the Chemical Engineering Department he worked on smokes 
for the Government’s Chemical Warfare Service. He measured smokes, 
smoke penetration, and smoke filters. Then he became interested in the 
problem of icing of airplanes and went to work on that in the Meteorology 
Department, for the Air Force. 


Meanwhile he had been doing some work on the side in supercooling. 
He found that by making an emulsion of water drops suspended in oil, he 
could cool water far below the normal freezing point, and it would not 
freeze i a certain point was reached, when the whole mass froze very 
rapidly. 62 

Early History -8- 

Vonnegut joined the staff of the Research Laboratory in the Fall of 
1945 and he continued his supercooling investigations there. 


In various contacts with Langmuir and Schaefer, Vonnegut learned of 
the work they were doing. Knowing that Schaefer was already working on the 
supercooling of water, he switched his activity to the supercooling of metals, 
in order to avoid duplication. He found he could supercool Woods metal by 
subdividing it into many small, independent particles, and he developed a 
technique of studying the effect with x-rays. He also-worked with tin, (62) 


Vonnegut had been interested in the work being done by Langmuir and 
Schaefer and had kept in rather close touch with it. In the fall of 1946, Lang- 
muir asked him if he would be interested in helping with the quantitative work 
being done on the number of ice crystals produced by dry ice. As a result, 
Vonnegut applied himself to this and other problems in the general study of 


It occurred to Vonnegut that some substance very similar to ice in its 
crystal structure might serve as the nucleus for the formation of ice crystals 
in the cold box. He went through all the known tables of crystal structure and, 
from over a thousand compounds, selected three substances that he thought 
might have possibilities: lead iodide, antimony and silver iodide. 56 

He dropped samples of each of these three substances into Schaefer’s 
cold box. The results were almost negligible, although he produced enough 
effect with the lead iodide to warrant further experiment. He and Schaefer 
tried iodoform and iodine and obtained ice crystals in small numbers with 
them, too, but nowhere near as many as with dry ice seeding. 

The problem intrigued Vonnegut. He decided to try a metal smoke in- 
stead of the powder. He introduced some silver smoke into the box by draw- 
ing an electric spark from a piece of silver, and it produced in the cold box 
a swarm of ice crystals. 

The results were So spectacular that he decided to try silver iodide 
again, but this time as a smoke, for the effect with silver did not persist. 
First he vaporized silver iodide and then he introduced into the cold box 
the smoke resulting from the rapid condensation of this vapor. It was a com- 
plete success. Further investigation showed that his earlier negative results 

Early History 29 

with silver iodide had been caused by the fact that the silver iodide he had 
used was impure. Powdered silver iodide worked very well when it was 
reasonably pure. He also found that the reason for the successful use of 
iodine was again impurity--contamination with silver. 

The problem then became one of finding out something about how 
silver iodide worked and of finding methods of generating silver -iodide 
smoke of small particle size on a large scale. So many nuclei could be 
produced with silver-iodide smoke that calculations indicated all the air 
of the United States could be nucleated at one time with a few pounds of 
silver iodide, so that the air would contain one particle of silver iodide 
per cubic inch--far more than the number of ice nuclei occurring nor- 
mally under natural conditions. 65 


Meanwhile Schaefer and Langmuir had continued their study of 
the effects of dry ice. In August of 1946 Langmuir made a theoretical 
study of the rate of growth of the nuclei produced by dropping pellets 
of dry ice through clouds of supercooled water.(80) He calculated the 
velocity of fall and time of dissipation of the dry ice, the amount of ice 
particles that would be formed, their size, the amount of snow which 
would result, etc. With a reasonable number of pellets dropped along 
a flight path into the top of a cloud, the limiting factor would not be the 
number of nuclei but the rate at which they could be distributed through= 
out the cloud. 

He also showed that such a formation of ice and snow particles 
would raise the temperature of the cloud, and he calculated the amount 
of temperature change. Thus the air in the cloud would be caused to 
rise, increasing its upward velocity because of the seeding. The result- 
ing turbulence would spread the ice nuclei throughout the cloud. He 
anticipated that it would only be necessary to seed a stratus cloud along 
lines one or two miles apart in order to give complete nucleation of the 
cloud within'a period of 30 minutes or so. 


Thus the stage was set for actual experiment with an airplane in 
real clouds. On November 13, 1946, a Fairchild airplane was rented at 
the Schenectady airport, piloted by Curtis Talbot, and Schaefer went 
aloft in search of a suitable cloud. 38) It was found over Pittsfield, 
about 30 miles east of Schenectady, at an altitude of 14,000 feet anda 
temperature of -200C. What happened next is best described by the 
following extract from Schaefer’s laboratory notebook entry for that 

Early History -10- 

‘“‘Curt flew into the cloud and I started the dispenser in 
operation. I dropped about three pounds (of dry ice) and then 
Swung around and headed south. 

‘‘About this time I looked toward the rear and was thrilled 
to see long streamers of snow falling from the base of the cloud 
through which we had just passed. I shouted to Curt to swing 
around, and as we did so we passed through a mass of glistening 
snow crystals!....We made another run through a dense portion 
of the unseeded cloud, during which time I dispensed about three 
more pounds of crushed dry ice..... This was done by opening 
the window and letting the suction of the passing air remove it. 
We then swung west of the cloud and observed draperies of snow 
which seemed to hang for 2-3000 feet below us and noted the 
cloud drying up rapidly, very similar to what we observe in the 
cold box in the laboratory..... While still in the cloud as we saw 
the glinting crystals all over, I turned to Curt and we shook hands 
as I said ‘We did it!’ Needless to say, we were quite excited. 

‘“‘The rapidity with which the CO, dispensed from the window 
seemed to affect the cloud was amazing. It seemed as though it 
almost exploded, the effect was so widespread and rapid........ 

‘“When we arrived at the port, Dr. Langmuir rushed out, enthu- 
siastically exclaiming over the remarkable view they had of it in 
the control tower of the G.E. Lab. He said that in less than two 
minutes after we radiced that we were starting our run, long 
draperies appeared from the cloud vicinity.”’ 

This first seeding flight was of tremendous significance. Not only did 
it show that the laboratory experiments and calculations were justified, but 
it also contributed new material to the rapidly accumulating store of know- 
ledge. For example, it suggested that the veil of snow that first appeared 
immediately below the cloud could not have been produced by snow falling 
from the cloud but rather was produced directly by the action of the dry 
ice pellets falling inte a layer of air below the cloud which was saturated 
with respect to ice but not with respect to water. 

Subsequent experiments proved that it was also frequently possible to 
seed a supercooled cloud by flying just below it and dropping dry ice. The 
thickness of the layer in which such seeding is possible is about 10 meters 
for each degree C below the freezing point at the cloud base. The ice crys- 
tals thus formed may be carried up into the cloud if the cloud is actively 
growing by convection. 

Early History -11- 

On November 21 Schaefer seeded a supercooled valley fog with dry 
ice. He found that it was possible to reduce visibility by generating more 
ice crystals than fog droplets and also to dissipate the fog by dispensing 
. just enough ice crystals to use up the fog droplets, each crystal growing 
‘large enough to fall to the ground. 


There were two other seeding flights made by Schaefer with a rented 
plane that month, one on the 23d and the cther on the 29th. 79) These tests 
were made on isolated cumulus-type clouds. The whole of each cloud was 
changed into ice within five minutes, and snow began falling from the base 
of the cloud. 

Photographs were taken from the ground every 10 seconds, and these 
were developed and projected as movies. They showed that, with orographic 
clouds the air moves into one part and leaves another part; ina matter of 
five minutes or So an entirely new mass of air is within the cloud. Thus 
it was found that experiments with small cumulus clouds are usually of 
little interest, for the effects last but a few minutes. 

cigs flight test was made on December 20, also using a rented 
plane. 2) This time the sky was completely overcast, and by 9 o’clock 

in the morning the Weather Bureau in Albany reported that it expected 
Snow by 7.0’clock that evening. Schaefer dropped about 25 pounds of 
granulated dry ice in the lower part of the cloud at a rate of 1 to 2 pounds 
per mile, about 1000 feet above the irregular and ragged base of the over- 
cast, at altitudes ranging from 7000 to 8500 feet, at about noontime. A 
two-pound bottle of liquid carbon dioxide was also discharged into the 
cloud during this period. 

Before and during the seeding flight, a light drizzle of supercooled 
rain had been encountered, which seemed to evaporate before it reached 
the ground. Flying back along the line of seeding, after seeding was com- 
pleted, it was found that the drizzling rain had stopped and that it was 
snowing. But on reaching the point where the seeding had stopped, drizzle 
conditions were again encountered. Three more seeding runs were made 
along the same line before the plane returned to Schenectady. 

The plane then descended to 4000 feet, where the visibility was 
better, and made a reconnoitering flight, checking the places where snow 
was falling. By this method and through reports received, it was found 
that snow started to fall in many places in the region. At 2:15 p.m, it 
started snowing in Schenectady and at many other places within 100 miles. 
It snowed at the rate of about one inch per hour for eight hours, bringing 
the heaviest snowfall of the winter. While the seeding group did not 

Early History -12- 

assume it had caused this snowstorm, it did believe that, with weather con- 
ditions as they were, they could have started a general snowstorm two to 
four hours before it actually occurred, if they had been able to seed above 
the clouds during the early morning. 


This, then, was the situation in which the research workers found 
themselves by the end of the year: Their work on precipitation static, 
then on aircraft icing, had developed through cloud studies into meteoro- 
logical work of profound significance. But, while their work on precipita - 
tion static and aircraft icing had been done under government contract, the 
work they were now doing on weather research was not. Their last con- 
tract had expired at the end of the previous June. 

At this point Dr. C. G. Suits, Director of the Research Laboratory, 
reported some of the results of cloud seeding to General Electric officials. 
While it was clear that weather modification and experimental meteorology 
were remote from the research which had been the traditional interest of 
the laboratory and the Company, it was equally clear that these new results 
were possibly of very great significance to the country. It was, therefore, 
decided that the work should be encouraged and pushed forward. 

Because the results might have such wide application to the country 
generally, and because much government assistance would be needed in the 
form of weather data, airplanes, and flight equipment, a government con- 
tract for the continuation of the work was to be sought. While the govern- 
ment agency which had sponsored the previous research was not interested 
in the new work, other government agencies were. Normal contacts with the 
Signal Corps, for example, had kept that organization in touch with the new 
research, and Col. Yates, chief of the Air Weather Service, had asked the 
Company to submit a bid covering this work in the latter part of September. 
A formal proposal covering cloud modification and cloud particle studies 
was submitted to the Evans Signal Laboratory at Belmar, New Jersey 
(a Signal Corps unit) on September 20. Meanwhile the weather studies were 
being conducted at General Electric expense, although General Electric anti- 
cipated no benefit resulting to the Company from the work from a meteoro- 
logical standpoint. 

The flight test of December 20 added a powerful stimulus to the Com- 
pany’s negotiations with the government. Although the General Electric press 
release covering it did not claim that the general snowstorm was caused by 
the seeding, the coincidence of the two events did cause some independent 
Speculation over the possibility of cause and effect. 

Early History -13- 

This question was So important that it was brought by Suits to the 
attention of Vice President R. E. Luebbe, general counsel of the Company. 
It was recognized that the possibility of liability for damage from cloud- 
seeding experiments was a very worrisome hazard in this new form of 
cloud experimentation. Since such a threat to the share owners’ money 
would not be balanced by any known gain to the Company’s products or 
business, there was great reluctance to incur risks of uncertain but 
potentially great magnitude. 

It was considered particularly important for this reason that any 
seeding experiments be conducted under government sponsorship. No 
further seeding flights were made until such sponsorship was provided. 

A contract (W-36-039-sc-32427 req. EDG 21190) was finally re- 
ceived from the Signal Corps covering ‘‘research study of cloud particles 
and cloud modifications’’ beginning February 28, 1947. It covered cloud 
modification by seeding, plus investigations of liquid water content, par- 
ticle size, particle distribution, and “‘vertical rise of the cloud in respect 
to the base.”’ 

An important part of the contract was a subparagraph stating that 
‘the entire flight program shall be conducted by the government, using 
exclusively government personnel and equipment, and shall be under the 
exclusive direction and control of such government personnel.’’ The Re- 
search Laboratory immediately notified all those involved in the research 
‘‘that it is essential that all of the G.E. employees who are working on this 
project refrain from asserting any control or direction over the flight pro- 
gram. The G. E. Research Laboratory responsibility is confined strictly 
to laboratory work and reports.”’ 

Although the contract was a Signal Corps contract, the project actu- 
ally had joint sponsorship by the U.S. Army Signal Corps and the Office of 
Naval Research, with the close-cooperation of the U. S. Air Force, which 
furnished airplanes and the associated personnel. 

The title of Project Cirrus was not applied immediately. It went into 
effect officially on August 25 of that year. 



The work done on Project Cirrus and the activities leading up to 
it were covered by several contracts with the government. 

The two research projects, involving first the work on gas masks 
and smoke filters and then the work on smoke generators, extended over 
a period from October 1940 through February 1944. This work was done 
under two contracts (NDCre-104 and OEMsr-131) with the Office of 
Scientific Research and Development. 

From October 1943 through June 1946, precipitation static research 
was carried on under Signal Corps contract W33-106-sc-65 and, subse- 
quently, under Air Force contracts W33-038-AC-9151 and W33-038-AC -15801. 

The meteorological research. which became Project Cirrus, was 
supported for a time by the General Electric Company. In February 1947, 
the first of three Signal Corps contracts (W36-039-sc -32427, W36-039-sc- 
38141, and DA36-039-sc-15345) was signed. The last of these remained 
in force until the end of September 1952. 


The over-all direction of the project and the formation of broad 
matters of policy were entrusted to a Steering Committee, consisting 
of representatives of the three military branches of the government co- 
operating in the project. Dr. Irving Langmuir and Dr. Vincent J. Schaefer 
of the Research Laboratory served as consultants on the committee. The 
military personnel was as follows: 

Signal Corps. Dr. Michael J. Ference, Jr., chief, meteor- 
ological branch, Evans Signal Laboratory, 
Belmar, N. J. His alternate was Dr. C. J. 
Brasefield of the same unit of Belmar. 

Navy. E.G. Droessler, geophysical branch, Office 
of Naval Res., Navy Department, Washington. 
His alternate was Commander R. A. Chandler. 

Getting Organized =16< 

Droessler was succeeded in the summer of 1950 
by Lt. Max A. Eaton. Commander Chandler was 
succeeded in the summer of 1949 by Commander 
G.D. Good, DENO©. (Air). 

Air Forces. Major P. J. Keating, chief, Weather Equipment 
Flight Test Facility, Middletown, Pa. Major 
Keating was succeeded 3/23/49 by Col. N.C. 
Spender of the Air Weather Office, Washington. 
Major Keating had no alternate; Col. Spender’s 
alternate was Lt. Col. J. Tucker of the Elec- 
tronics & Atmospheric Branch at Washington. 

The activities of Dr. Langmuir, Dr. Schaefer, Dr. Vonnegut, and others 
of the General Electric Company’s Research Laboratory staff were limited 
by the Steering Committee to laboratory work and analysis. The General 
Electric scientific group came to be known to the personnel of the project 
as the Research Group. In addition to Langmuir, Schaefer, and Vonnegut, 
this group included Messrs. Kiah Maynard, R. E. Falconer, Raymond Neu- 
bauer, Robert Smih-Johannsen, Duncan Blanchard, George Blair, Myer 
Geller, Victor Fraenckel, and Charles Woodman. 

An Operations Group was established by the Steering Committee early 
in the life of the project to plan, co-ordinate, and control all project air oper- 
ations, aSsist in the assembly and analysis of all technical data obtained, 
provide all necessary meteorological information and service required for 
the efficient conduct of the project, and take whatever action was necessary 
to fulfill those requirements. This group would contain all military and 
civilian personnel necessary to fulfill those functions, and it would be under 
the direction of an Operations Committee. This committee was set up to 
‘‘assume full responsibility for, and, therefore, exercise complete freedom 
of action in the initiation of plans for, and the control of, all project air oper- 
ations to be conducted in the vicinity of Schenectady.’’ 

The Operations Committee was set up, like the Steering Committee, to 
include representatives of the three services, plus Kiah Maynard of the Re- 
search Laboratory as General Electric consultant. It went through numerous 
changes of personnel. The initial membership, and subsequent changes, were 
as follows: 

1. Lt. Comm. Daniel F. Rex, USN, chairman; Capt. C. N. 
Chamberlain, USAF; Roger Wight, Signal Corps; Mr. 

2. Wight was succeeded by Samuel Stine in August, 1947. 

Getting Organized -17- 

3. In June, 1948, Mr. Stine became chairman and Lt. Comm. 
ih, B, Faustwexecutive officer. 

4, In the fall of 1948 Major Rudloph C. Koerner, Jr. became 
chairman, Rex and Stine left the committee, and Capt. J. A. 
Plummer, USAF, was added. 

5. In February, 1949, Lt. Comm. Paul J. Siegel became ex- 
ecutive officer and Lt. Comm. Faust, operations officer. 

6. In April, 1949, Faust was succeeded by Capt. Carl F. Wood 
as operations officer, Faust becoming data control officer. 
Plummer left the committee. Membership from then on: 
Koerner, Siegel, Wood, Faust, Maynard. 

The initial personnel of the operations group consisted of six repre- 
sentatives of the Signal Corps, six of the Air Force, and six of the Navy. 
Although the number of General Electric people working on the project re- 
mained fairly constant at a figure of six or seven, the government repre- 
sentatives varied widely in number. As a consequence, the total personnel 
of the project varied also, running as high as 40 or 41 persons at various 
times when activities were at their peak. These included crewmen for the 
planes, weather technicians, and civilian employees for such services as 
photography. A total of 33 persons went on the Puerto Rico operation, and 
37 went on the second trip to New Mexico. 

An alphabetical list of the members of Project Cirrus at one time or 
another is attached as Appendix |. 


At the outset, and until June 1, 1947, Project Cirrus test flights were 
made by a plane from the Weather Squadron assigned to the Signal Corp. 
This plane visited Schenectady six times, and a total of five seeding flights 
were made. Olmsted Field at Middletown, Pennsylvania, was the base of 

It was Soon discovered, however, that many delays in carrying out 
flights could be traced to this geographic separation of the Operations 
and Research groups. Accordingly, in the summer of 1947, all flight 
operations were transferred to Schenectady. Headquarters for the Opera- 
tions Group was established at the General Electric hangar at the Schen- 
ectady County Airport. 

The facilities steadily expanded until, at the end of 1948, they con- 
sisted of a total of 1830 square feet of office, operations, and storage 

Getting Organized -18- 

space, including a flight tower, weather office, administration office, dark 
room, navy cage, Recordak room, operations office, analysis room, and 

a parachute-and-stock room. In addition to this, about 640 square feet of 
conference room was available whenever required. In the same category 
was a room in the hangar for aircraft, when a heated area was needed for 
installation work, repairs, or other reasons. 

On call were two aircraft mechanics, two shop men, two transcribers, 
and an instrument man. A full-time secretary handled reports, correspon- 
dence, telephones, etc. 

To facilitate flight operations, two Weather Bureau teletype circuits 
were installed, as well as a Teletalk system connecting all offices. This 
could also operate a public-address system in the hangar and the ramp. In 
addition, connections were made through two leased wires to the Boston CAA 
control center and the Army Airways control center at Middletown, Pa. 

At the hangar, a repair station was available. Guards were assigned 
for the protection of aircraft and equipment, and standard aircraft fire- 
fighting equipment with trained personnel was on hand for emergencies. 

At first the number of aircraft assigned to the project was disappoint- 
ingly meager, but eventually this situation was corrected. At one time as 
many as six planes were available--three from the army and three from 
the navy. 

Active flight operations ran from the establishment of the project in 
March, 1947, until August, 1950, when the Operations Group was disbanded 
at the suggestion of the Research Group. (This move was made in the inter- 
ests of economy, for most of the objectives of the flight program had by that 
time been accomplished.) 

A list of all the flights made by Project Cirrus is attached as Appendix 
II,. This list includes the flights made in rented planes before the establish- 
ment of the project. It also includes the flight numbers for the time after a 
system of numbering was instituted. 

Although a brief statement of the location and purpose of each flight 
is also given in Appendix Tl, this information is not supplied in detail. It is, 
rather, summed up in connection with the discussions which follow of the 
individual studies and operations. Detailed descriptions of the flights are 
available in flight folders located, at the time of this writing, in the files 
of the Weather Station in the Laboratory penthouse. 

Getting Organized -19- 


In addition to the flight program, the Operations Group had the re- 
sponsibility for condicting numerous operations on the ground, These 
operations were of two kinds: photography and silver iodide seeding. 

When it became apparent that such operations would be necessary as 
part of the project from time to time, a system of numbering each operation 
was established. A record of all the numbered ground operations was main- 
tained by the Operations Group, and a tabulation from this record is attached 
as Appendix III. 


Weather observation being essential to operations of the type carried 
on by Project Cirrus, one of the first steps to be taken by the Operations 
Group was to set up a complete weather-observing station as part of the fa- 
cilities at the General Electric hangar. Daily radio contact was established 
with the Weather Equipment Flight Test Facility at Middletown, Forney ivenla, 
and circuits for weather teletype services were installed. 

The primary requirements of the weather station were agreed to be as 

1. Preparation of aerological flight data prior to take-off 
on flight tests. 

2. Gathering of data to supplement that obtained in the air 
on seeding missions, gathered after the flight for the area 
concerned during the time of test. 

3. Co-operating with the Research Group in its study of weather- 
analyzing instruments and test flights, and supplying it with 
such special weather reports as needed for analyzing purposes. 

In order to meet these requirements, the Weather Station performed 
the following functions: 

1. Daily small-cloud maps were prepared of conditions dur- 
ing the last hour before take-off on test flights, covering 
an area having a radius of 200 miles from the Schenectady 
County Airport. 

2. Daily flights were made to record the air conditions up 
to 8000 feet above the airport. 

Oo eae 

Getting Organized -20- 

3. Radiosonde data above freezing level were obtained daily 
from Albany. 

4, Daily surface weather maps were prepared of the com- 
plete Eastern United States area. 

5. Data were obtained daily of the winds aloft for the Eastern 
United States. 

6. Local actual weather observations were made hourly. 

7, After each test flight, cross-sections of the areas seeded 
were prepared, based on reports of flight personnel and 
teletype weather reports. 

When the Operations Group was disbanded in 1950 and the facilities at 
the General Electric Hangar were abandoned, the Weather Station was trans- 
ferred to the penthouse of the Research Laboratory at the Knolls. 

Through the Office of Naval Research, two navy men had a lengthy 
assignment to the project as aerologists, and as such they contributed much 
valuable assistance to the study of general and specific problems encountered 
in the various research studies. These men were Lt. (jg) W. E. Hubert and 
H, J. Wells, AGC. (Lt. Hubert was succeeded in 1951 by Lt. Cdr. C. E. Tilden.) 
A partial list of studies made by these men is included on pages i and ii of the 
ano ewe yoo the final report on Contract W-36-039-sc-38141 dated July 
SOs 1951) 


Another very important activity essential to the success of the project 
was photography of various kinds, From the outset it was found that complete 
evaluation of the results of the various seeding experiments could not be 
made without taking pictures. 

Both still and motion-picture types of photography were used, In addi- 
tion, special techniques were adopted. For example, by means of lapse-time 
photographs it was possible to speed up movies in order to obtain a better 
grasp of the changes taking place in a cloud. Also, by the use of stereoscopic 
equipment, it was possible to produce three-dimensional views. 

A photographic darkroom was provided as part of the Ground Operations 
facilities at the General Electric hangar. When the Operations Group was dis- 
banded in 1950, darkroom facilities were provided in the penthouse weather 
station at the Knolls. 

Getting Organized -21- 

So important was photography considered in the active phase of the 
project, when the Operations Group was functioning and regular test flights 
were being conducted, that many civilian professional photographers were 
employed in addition to those provided by the Signal Corps. On the second 
New Mexico test operation, six photographers made the trip from Schenectady 
to Albuquerque. During the Puerto Rican test operation, over 100,000 
frames of lapse-time pictures were taken in color. The load on the darkroom 
at the General Electric hangar in Schenectady became So great that a photo- 
graphic trailer was obtained from the Signal Corps Engineering Laboratories 
to relieve the congestion. 

One print of each photograph was, at the time of the preparation of 
this report, on file in the Knolls penthouse weather station, plus virtually 
all motion pictures (some are in the possession of Schaefer). All negatives 
are filed in the photographic vaults of the Signal Corps Laboratory at 
Belmar, New Jersey. 


A considerable portion of the time and activity of Project Cirrus per- 
sonnel was spent on the development of special instruments, tools, and equip- 
ment essential to the project. As in any new undertaking in which there is 
little or no previous experience, many new devices of this type had to be 
designed, or old ones had to be adapted to special requirements. In addi- 
tion to Schaefer’s simple cold chamber, which became a standard item of 
meteorological research in the field of cloud physics, the more important 
equipment of this type follows: 

Dry Ice Dispenser. One of the first instruments which had to be de- 
veloped was an automatic dry ice dispenser. 79) This was devised 
(Schaefer -Falconer-Kearsley) for use in an airplane, to allow a continuous 
release of dry-ice pellets during seeding operations. 

Dry Ice Crusher. This was a device (Schaefer-Falconer -Kearsley) 
for reducing blocks of dry ice to usable fragments for seeding purposes. 
It greatly reduced the time required for preparing this material for a 
seéding run. 


Silver Iodide Generators. A number of different methods for the gen- 
eration of silver-iodide smokes were studied by Vonnegut early in the his- 
tory ve ike project. One method vaporized silver iodide from a het fila =1>n 
ment. 3 Another involved the use of a small electric furnace. o) A 
third method vaporized silver iodide from a string in a flame and then 
caused a very fine smoke by rapidly quenching the flame with a blast of 
compressed air. 56) A fourth introduced silver iodide into flares of the 

Getting Organized -22- 

standard fireworks type.(57) A fifth technique produced silver-iodide smokes 
by first producing a silver smoke with an electric arc and then converting 
the silver. pe panucks to silver iodide by the addition of iodine vapor to the 

In addition to these, two other techniques were devised which were well 
suited to large-scale seeding. In one, a solid fuel, such as charcoal, impreg- 
nated with a silver-iodide solution, was burned.\°7,68) The silver iodide 
vaporized and then condensed in the form of a fine smoke. In the other tech- 
nique, a Solution of silver iodide and acetone was atomized in a spray nozzle 
and burned, vaporizing the silver iodide. 73) The silver-iodide vapor 
rapidly condensed when it mixed with the cool air of the atmosphere, to form 
a smoke of very small particles, the size of which could be varied over a wide 
range. A later design of this generator, adapted for use in flight, was found 
to be simple and reliable. 

Camera Clinometer. It became evident in early flights that it would be 
necessary, when photographing seeded areas, to know the vertical angle at 
which the camera was pointed. A very simple device was made (Langmuir- 
Falconer) to attach to the camera to indicate this angle. i 

Flight Instruments. Standard instruments often had to be modified, 
and new ones were occasionally developed. For example, a device was 
evolved (Maynard-Falconer) to record the movement of the airplane ‘‘stick’’ 
for correlation and measurement of vertical acceleration. 

‘‘Weather’’ Instruments. But it was in the field of weather observation 
and atmosphere studies that most of the instrument development occurred. Some 
of the early devices were special rods (Falconer-Maynard) to be mounted on 
the airplanes to determine the rate of icing; 75) an air decelerator (Schaefer- 
Falconer) to assist in sorting out rain, snow, dust, or cloud particles from the 
eee as the plane passes through; 5 ) and a cloud- particle gun 

(Se tetas yeteon) for sampling the cloud-droplet size distribution in 

clouds. An attempt was made to develop a cloud-particle ranging instru- 
ment for airplane use to provide a continuous record of the distribution of 
particle sizes in a cloud, but without success. 

Cloud Meter. An important early development was a cloud meter 
(Schaefer-Falconer), designed to provide information which would give a 
eS Ue oi; he th Boy ae effective particle sizes in the various portions of a 
cloud. This device, embodying a continuously moving tape im- 
pregnated with a water-sensitive dye, gave a satisfactory indication of the 
amount of cloud particles collected. 

Condensation Nuclei Detector. Another important instrument (Vonnegut) 
was one for obtaining a continuous record of the concentration of condensation 
nuclei in a given air sample. 67) This involved a Simple adaptation of the 

Getting Organized -23- 

cloud-chamber technique. Also a very simple pocket-size unit was devised 
for making spot checks of the relative numbers of such nuclei in a given 

Vortex Thermometer. A development of much significance was the 
design by Vonnegut of an instrument, the oe thermometer, for use by 
airplanes in measuring true air temperature. 66) The usual type of ther- 
mometer is unsatisfactory for this purpose because of aerodynamic heat- 
ing caused by the rapid movement of the airplane through the air. The 
vortex thermometer reduced these aerodynamic effects to a negligible 
amount. Also, for the first time, it made it possible to give a quite accu- 
rate measurement of the temperature in a cloud. Furthermore, an indica- 
tion of true air speed can be provided by measuring the difference in 
readings given by a vortex thermometer and one exposed in the normal 
manner, because the deviation from true temperature of a normal ther- 
mometer varies with the speed of the plane. But it was found that the 
vortex whistle (see below) showed greater possibilities for this application. 

Vortex Speed Indicator. An outgrowth of the development of the 
vortex thermometer was the adaption of the principles involved to the 
production of a musical note (Vonnegut). As the pitch of the note produced 
in such a manner varies with pressure, such a whistle could be used as 
the basis for measurement of true air speed and air mileage of airplanes, (71) 

Rain Catcher. A tool found very useful in rain studies aloft was a 
rain catcher, developed (Langmuir-Schaefer-Maynard) to give the average 
value of the precipitation in the air for approximately each thousand feet 
of flight. ‘The device involves the use ofa rain scoop, a tube whose exit 
velocity can be controlled, and a group of Storage containers. 82 

Portable Cold Chamber. A simple but effective cold chamber was 
designed by Schaefer, which could be carried about for field studies. It 
consisted of a small rectangular wooden box lined with copper sheeting 
and having a copper inner chamber. A charge of five pounds of crushed 
dry ay was found to hold the temperature below -10°C for three 

Ice Nuclei Detectors. Since one of the important properties of the 
atmosphere as related to the persistence of supercooled clouds is the 
presence of ice-forming nuclei, considerable effort was expended toward 
the development of an instrument which would provide a continuous, auto- 
matic record of the quantity of such nuclei in the air at any given time. 
Two developmental instruments were devised, but difficulties were expe- 
rienced with both of them, and neither was brought to a satisfactory 
degree of perfection. One device (Schaefer) made use of the tendency 

Getting Organized -24- 

of a thin water-soluble film of polyvinyl alcohol to supercool. (41) The other 
(Vonnegut) utilized the cooling effect of the ice crystals when they struck a 
hot wire carrying an electric current. 

Uniform Particle Generator. A useful tool in the study of cloud physics 
is an apparatus for producing particles of uniform size, developed (Vonnegut) 
during the work on one of the ice nuclei detectors. 70) With it, particles were 
produced in sizes down to about 10 microns diameter. 

Salt Particle Detector. An apparatus was constructed (Vonnegut- 
Neubauer) that detects and counts aerosol particles, such as salt particles, 
by the pulses of light they produce when they enter a hydrogen flame. Ob- 
servations showed that the concentration of large sodium-containing particles 
in the atmosphere is subject to considerable fluctuation,(74A 

Cloud Chamber. A very simple but effective adaptation of the con- 
tinuous eu i ee was developed by Schaefer, using water instead of 
aleohols* =? It gave promise of considerable value in conducting quanti- 
tative experiments with a controlled atmosphere. 

Aerosol Precipitator. A very simple apparatus was constructed by 
Vonnegut to precipitate aerosol particles from the atmosphere on a strip 
of paper. It was found useful in the study of condensation nuclei in the at- 

Snowflake Recorder. This device was developed (Schaefer-Falconer- 
Kearsley) to record the type and concentration of snow crystals reaching the 
ground during the storm period of the winter season, It utilizeda strip of 
paper on which was rubbed a water-sensitive dye. 78 

Cloud Type Indicator (Schaefer-Falconer), By measuring the daylight 
from a small portion of the northern sky, it was found that the variations in 
reflection caused by blue sky or various cloud types which passed this area 
Bose at a curve which could be interpreted in terms of particular types of 


The interest and activity in cloud seeding and the fundamental physics 
of clouds, following the initial experiments, were so varied that it is diffi- 
cult to.give an orderly account of the progress in this field, Research both 
in the laboratory and in the atmosphere continued to reveal new and inter - 
esting facts. The contents of this section of the history consist of summaries 
of the more important laboratory studies in this field which were conducted 
by the Research Group of Project Cirrus. 


It would be difficult, if not impossible, to list the names of all the 
people contributing to the laboratory studies of the project. But twelve 
persons should be mentioned who took part, either continuously through- 
out the life of the project, or at one time or another during its existence. 

Dr. Irving Langmuir, under whose direction the project evelved, 
planned the methods and techniques for the various programs, analyzed 
flight results, and set up procedures for the routine analysis of such re- 
sults. He also reduced to convincing mathematics many of the theories 

Dr. Vincent J. Schaefer, who worked with Langmuir in the planning 
of the project, carried out both field and laboratory experiments on the 
fundamental processes involved in changes of cloud forms, 

Dr. Bernard Vonnegut also carried out extensive field and labora- 
tory experiments on subjects associated with the project. Particularly 
he concentrated on theories and techniques associated with the use of 
silver iodide for seeding. 

Raymond E. Falconer worked on various phases of instrumentation 
of the flight planes, on laboratory studies, and on other related problems. 
He worked closely with Langmuir in his periodicity studies. After the 
termination of the Operations Group, the establishment and maintenance 
of a weather station in the Knolls penthouse was his primary responsibility. 

Victor Fraenckel served as General Electric representative on the 
Steering Committee and as contract liaison. 

Kiah Maynard was the Research Laboratory representative on all 
flight tests and on the Operations Group when it was active. He gathered 
data and maintained records of all flight tests. He was associated with 
Falconer in the operation of the weather station at the Knolls penthouse. 

Laboratory Studies -26- 

Raymond L. Neubauer was associated with the later stages of the project 
in the development of instruments and studies of silver-iodide smokes. 

Robert Smith-Johannsen, associated with the project during its earlier 
history, was principally concerned with the study of the supercooling of water. 

Duncan Blanchard was temporarily associated with the project in con- 
nection with the study of water droplets. 

Myer Geller, temporarily associated with the project, contributed im- 
portant calculating work. 

Charles Woodman, temporarily associated with the project, contributed 
important mathematical work. 

Arthur Parr, a Research Laboratory machinist, built almost all the 
special equipment and developmental instruments involved. 


One of the most important phenomena associated with the study of the 
physics of clouds is the formation, distribution, and relative abundance of 
nuclei for the formation of ice crystals. This subject, therefore, occupied 
the attention of the principal members of the Research Group to a greater 
or less extent throughout its history. 

Considerable work was done in developing instruments and methods 
for detecting the presence of, and counting, such nuclei in the atmosphere. 
Relatively early in the history of the project, a station was established by 
Schaefer at the Mt. Washington Observatory for regular observations of the 
concentration of such ice-forming nuclei, and these observations continued 
over five years. Subsequently, Schaefer found in the laboratory that certain 
kinds of soils, when dispersed a a dust, were moderately good nuclei under 
certain atmospheric conditions. 43 

At the time of writing this report, the number of ice nuclei needed in 
a supercooled cloud to initiate a chain reaction (see page 28) was not yet 
known, but evidence found early in the history of the project, suggesting 
that a critical concentration is found in the range of 10,000 to 50,000 nuclei 
per cubic meter, has consistently been strengthened since. o4 

Observations of ice nuclei were also conducted at the Research and 
Development Division of the New Mexico School of Mines at Socorro, with 
whom the scientists of Project Cirrus maintained a close liaison. 

Laboratory Studies -27- 

A significant fact resulting from the Mt. Washington studies was 
the rarity of Sal high concentrations of active ice-forming nuclei 
in the atmosphere. If the observed results are a true representation 
of the average mean condition of the atmosphere, it is obvious that, by 
the artificial introduction of sublimation nuclei into the atmosphere, man 
possesses a powerful method of modifying many cloud systems. 

One prolific source of ice-forming nuclei might be the Great Plains 
and the more arid regions immediately adjacent to the Continental Divide. 
Wind storms, dust devils, and strong convective ey could easily ac- 
count for the formation of ice-forming nuclei aerosols. 47) 

It Seems probable ey ie smoke produced by forest fires is a 
poor source of such nuclei. 47) An attempt was made to determine the 
role that bacteria and the spores of fungi might play in this respect (17) 
and to evaluate the role of industrial smokes of various’ kinds. 59) 

Adiabatic Expansion of Gas. An important contribution to the early 
knowledge of meteorological phenomena was made through Vonnegut’s 
observations that, when gas is cooled to below -39°C by adiabatic expan- 
Sion, very large numbers of ice crystals are formed.(60) For example, 
the low temperature praduced at airplane propeller tips and wings can 
seed supersaturated air or Supercooled clouds, resulting i persistent 
vapor trails or cloud modification. Cwilong had reported\® that ice 
erystals could be produced by this method, but he apparently had not 
appreciated the enormous numbers which are so produced. 

It was found that the adiabatic expansion resulting from the bursting 
of a rubber balloon a millimeter in diameter produced over 10,000,000 
ice crystals. Schaefer made a popgun which did the same thing, lending 
itself to careful control of temperature, pressure, and humidity. 

This provided corroboration of conclusions already reached with 
dry ice and furnished additional quantitative data which were found very 

Chemical Effects. An interesting effect noticed by Vonnegut while 
carrying out Some Studies of ice crystals in a cold chamber was that 
the presence of normal butyl alcohol caused the crystals to form as hex- 
agonal columns instead of hexagonal plates, (08) The phenomenon was 
studied by Schaefer in some detail, but no practical application of the 
findings was developed. 

Laboratory Studies -28- 

Spontaneous Formation. Work done by Schaefer and others as early 
as 1946 indicated that ice crystals formed spontaneously in water-saturated 
air when the temperature reached the neighborhood of -35 or -400C. Schaefer 
conducted quite a bit of research into this subject of spontaneous forme 
and determined that the critical temperature was -38.9+ 0.1 degrees. o4 

This phenomenon is probably of considerable significance in relation 
to the formation of cirrus clouds and ice crystal fogs in the free atmosphere. 

Structure. Schaefer’s study of the various types of snow crystals, which 
started before the establishment of Project Cirrus, continued throughout the 
project. In 1948 he published a simple yet seat list of ten types of solid 
precipitation for classification purposes, (39 In slightly modified form this 
classification is now in use throughout the world. ‘ 

Crystal Growth and Multiplication. Experiments made by Schaefer in 
1949 indicated that snow particles tend to shed minute fragments of ice when 
they are placed in air slightly warmer than their own temperature. An ice- 
forming nucleus appearing in a supercooled cloud grows rapidly, especially 
in the temperature range of -12 to -16°C, where the difference between the 
partial vapor pressure of ice and of water passes through a maximum. When 
the crystal becomes large enough, it sheds a considerable number of ice parti- 
cles as it falls through the cloud. These particles then serve as new nuclei 
and repeat the cycle. In this manner, a few ice-forming nuclei in a cubic 
meter of cloud may start a chain reaction which, within_a few minutes, could 
shift a supercooled cloud to a mass of snow crystals. 

A laboratory study was made to determine the factors of importance 
for obtaining the maximum rate of snow crystal growth. 


After the discovery that silver-iodide smokes serve as an excellent 
nucleus for the formation of ice crystals, the project was faced with the prob- 
lem of finding some way of generating the smoke efficiently and in quantity. 
It was found that smokes consisting of exceedingly fine particles could be 
easily produced by vaporizing silver iodide at a high temperature and then 
rapidly quenching the vapor. This was readily accomplished by burning 
Silver -iodide -impregnated charcoal or injecting a spray of silver-iodide 
Solution into a hot flame. Simple generators based on this principle were 
made which could produce 10 ?*nuclei per second--enough to seed from 
1000 to 10,000 cubic miles of air per hour (65 

Laboratory Studies -29- 

A very interesting fact discovered as the result of one of Vonnegut’s 
studies is that silver-iodide particles do not react immediately as ice- 
forming nuclei when introduced into a supercooled cloud of water droplets. 
Even 50 minutes after introducing a smoke sample into the cold chamber, 
ice crystals could be seen to form at a measurable rate. The general 
conclusion reached as a result of this study wee iat the rate of reaction 
at -18°C is 30 to 40 times faster than at 10°C, © 

The first unambiguous results in cloud seeding using silver -iodide 
generators were obtained in 1948. Silver-iodide nuclei produced by one 
of Vonnegut’s generators installed in an airplans resulted in cloud mod- 
ification similar to that produced by dry ice. 

Experiments were conducted to determine whether the burning of 
charcoal particles used in silver-iodide seeding from an airplane would 
be seriously affected by the moisture in clouds. It was concluded that 
the bumping is not seriously affected if the charcoal is thoroughly ig- 

Some experiments were conducted to discover the value of a turbo- 
jet burner as a Silver-iodide smoke generator. It was decided that such 
a method might &S of value if larger generators were needed than those 
already in use| 8) 

Experiments were also made in tracing silver-iodide smokes after 
their release by seeding generators. 6 

The nature of silver iodide is such as to suggest the possibility 
that its effectiveness as a seeding agent might be reduced by the action 
of ultraviolet and near-ultraviolet radiation from the sun. Accordingly, 
an investigation was made to determine its rate of decay under expected 
conditions of radiation in the free atmosphere. The results of work in 
this field not only by Project Cirrus, but also the New Mexico School 
of Mining and Technology, suggested that far greater quantities of silver- 
iodide particles might be required for seeding operations under conditions 
of bright sunlight than would be needed at night or under conditions of 
Cloud cover. But later work and observations indicatsd that the effect 
of sunlight might not be as bad as was forecast. ol,72 

Experimental work showed that it is possible to convert super- 
cooled ground fogs to ice crystals by releasing silver-iodide smokes. 


Laboratory Studies -30- 


Although many of the details are still lacking, studies conducted by 
Project Cirrus began to provide answers to the question of how rain is 

In 1947, when reports were received of successful results obtained 
by dry-ice seeding of cumulus clouds over Hawaii having a temperature 
above the freezing point, Langmuir restudied theoretical calculations he 
had prepared in 1944 in studies relating to work at Mt. Washington Ob- 
servatory. As a result ae developed a theory which agreed very well with 
the reactions reported, (/ ) 

According to Langmuir’s theory, actively growing cumulus clouds 
having an average drop size of 20 microns, a liquid water content exceeding 
2.5 G/M, and a vertical thickness of more than a mile are in favorable 
state for starting a chain reaction. This could be achieved by introducing 
water drops greater than 50 microns in diameter into the actively growing 
part of the cloud. 

Large drops in such a cloud would fall at a greater velocity than 
would small drops. In falling, they would overtake and collide with the 
small drops and thereby increase in size. In time the large drops would 
become so large that surface tension could no longer hold them together, 
and they would break up into two or more smaller drops. These in turn would 
grow and break up, and the number of large drops would increase in this 
manner by a chain reaction. 

The process would not be sufficient to produce large numbers of 
raindrops in a cloud without a vertical updraft. However, in the case of 
clouds with suitable updraft conditions, many stages of the chain reaction 
are carried out, resulting in the production of rain. 

This chain-reaction theory led Langmuir to postulate that cumulus 
clouds having sufficient updrafts could be seeded with a few large water 

To determine the validity of several of the important phenomena in- 
volved in this theory, various studies were initiated in the laboratory and 
experiments conducted in the field. Blanchard devised a splendid method 
for studying the properties of free-falling water droplets in air, using a 
vertical wind tunnel. A series of striking stroboscopic photographs was 
made, showing the oscillations, gyrations, Sree UE and fractures that go 
on as water drops fall at their terminal velocity. 

Laboratory Studies -31- 

Another activity concerned itself with devising means of sampling 
raindrops and measuring diameter. 3 

| Seeding with water drops was carried out with apparent success in 
tropical clouds. 41) This is more fully discussed in a later section of 
this report.(Page 48) 


Condensatién nuclei played an important role in the behavior of the 
atmosphere. In 1948 Vonnegut devised a method of obtaining a continuous 
record of the concentration of condensation nuclei in the atmosphere, (©7 
Various experiments were conducted with this equipment, both aground 
and aloft. The results suggest that the continuous measurement of the con- 
centration of condensation nuclei may be very useful in meteorological in- 


It was observed in 1943 by Schaefer that interesting atmospheric 
electrical measurements could be obtained by connecting one end of a 
shielded cable to an insulated needle presented to the sky and the other 
end to a Suave recording microammeter, one side of which was well 
grounded, Among the interesting observations made during successive 
years was one to the effect that the data obtained with this instrument in- 
dicated the passage of charged clouds over the observation point. 

Continuous records were kept by Falconer from 1948 on, using the 
data provided by this equipment, and an attempt was made to correlate 
the measured corona-discharge currents with other meteorological phe- 
nomena, such as frontal passages, wind direction, precipitation, and re- 
flected light from the northern sky. It was found that there was generally 
good agreement between such findings and those of other investigators. 

Best correlations obtained with this equipment seemed to be with 
frontal passages associated with the arrival of new air masses and the 
occurrence of precipitation not necessarily local but possibly extending 
to a radius of a few hundred miles. But correlation was also obtained 
with wind shifts and pressure changes, Since frontal passages were 
associated with those phenomena. There also seemed to be some re- 
lation between certain instrument indications and small, sharp changes 
in the ne een light from the northern sky, particularly in apparently 
clear skies | 

Laboratory Studies -32- 

Workman-Reynolds Effect. When Workman and Reynolds announced 
in 1948 their discovery of the formation of a large electrical potential when 
water containing small quantities of certain salts is in the process of 
freezing, Schaefer decided to check the experiments by an independent in- 
vestigation. Accordingly, test equipment was set up and observations were 

The Workman-Reynolds electrical effects were immediately observed. 
The results of this experiment have very important implications with re- 
spect to the development of lightning in thunderstorms. 

Electrical Atomization. Some qualitative experiments were made by 
Vonnegut and Sie ana ig determine the effects of high voltage on the form- 
ation of water drops. 74B) tt was found that streams of highly electrified, 
uniform droplets about 0.1 millimeter in diameter could be produced by 
applying potentials of from 5 to 10 kilovolts, ac or de, to liquids in small 
capillaries. Aerosols of uniform size and having a particle radius of a 
micron or less could be formed if the capillary was positively charged and 
if liquids having low electrical conductivity were used. Aerosols formed in 
this way showed the colors of higher-order Tyndall spectra. 


In connection with an investigation of snowstorm intensities, Schaefer 
started measuring variations in sky brightness using a light-sensitive instru- 
ment. Falconer subsequently carried on the measurements in more detail. 

It was discovered that the variations in the curve made by this instrument 
were a rather good indicator of the type of cloud cover prevailing during a 
day. There seemed to be a typical trace for each general cloud type. 

Such an instrument might be useful in automatic weather stations, to 
give some indication of sky conditions in remote locations. 

Test installations were made by Falconer at various points aground 
and aloft, and considerable data were gathered. 


Of great significance, both in connection with activities of the Research 
Group and with those of the Operations Group, was the analytical work per- 
formed by Langmuir. It constituted one of the most important contributions 
to the project. 

Laboratory Studies -33- 

From the outset he studied and analyzed the various test flights of 
the Operations Group, and extensive reports were prepared analyzing cum- 
ulus and stratus cloud seedings. His analysis of the cumulus seedings over 
Hawaii and the chain-reaction theory of rainfall which resulted have al- 
ready been mentioned. (Page 30) 

Langmuir paid particular attention to the seeding operations carried 
on in New Mexico, and to the possible effects of silver-iodide seeding, and 
these activities are described more fully in a later section of this report. 
(Page 47) 

Such a large quantity of data was accumulated by flight, field and 
laboratory activities during the more active period of the project, that the 
Research Group finally suggested early in 1950 to the Technical Steering 
Committee that flight operations be terminated at Schenectady in order 
that the accumulated data might be evaluated and reports prepared on 
the findings. 



The significance of cirrus clouds and the role they play in various 
weather phenomena were, of course, subjects of intense interest to Pro- 
ject Cirrus. Various studies of and experiments with such cloud forms 
were conducted, although more attention was paid to stratus and cumulus 

A regular daily observation program was begun in 1947 to explore 
the possibility of inducing the development of cirrus-type clouds under 
clear sky conditions. It was believed that supersaturation with respect 
to ice probably occurs fairly frequently at temperatures warmer than 
-39°C in air devoid of foreign-particle nuclei. Lacking such nuclei, a 
considerable degree of supersaturation could develop, as is often shown 
by the generation of so-called vapor trails behind high-flying aircraft. 

- To explore these possibilities, Falconer initiated a project in which 
balloons carrying dry ice in open-mesh bags were released on a daily 
schedule and followed by theodolite. Many of these produced visible trails 

of ice crystals, and in several instances the trails were quite notice- 
Bic oo, 18) 

Several seedings were also carried out from an airplane in clear 
air, using both dry ice and silver iodide. In clear air supersaturated 
with respect to ice, the seeding operation produced a cloud made of ice 
erystals. The results of these operations indicated that, if the humidity 
is low, even at temperatures below -39°C, appreciable supersaturations 
with respect to ice can exist without the formation of ice crystals. Ice 
crystals can then be created, however, by seeding with either dry ice or 
silver iodide.\’3 : 

Natural Formation. In six of the Project Cirrus test flights a con- 
siderable effort was directed toward obtaining photographic evidence of 
the appearance of the tops of cirrus clouds. It was found that, despite the 
various irregularities seen from below, the top of such clouds is extremely 

Most meteorologists and weather students agree that a cirrus cloud 
formation is often associated with the overrunning of cold air by a warmer 
tongue of moist air. Whenever the moisture conditions in the warm over- 
riding air reach saturation with respect to water and the colder air below 
has a temperature of -39°C or colder, ice crystals will form spontaneously 
at the inversion interface. The number of primary crystals that form will 
depend on the concentration of condensation nuclei and ice nuclei in the 
moist air mass. The number and size of secondary crystals that form will 

Cirrus and Stratus Studies Ge 

probably be some multiple of the effective number of condensation nuclei. 
Since these conditions for the ice-crystal formation are of a marginal na- 
ture, the variability and often unique appearance of true and false cirrus 
clouds may be closely related to these spontaneous crystal formation 

Based on this reasoning, Schaefer concluded that it is likely that the 
concentration of supercooled water droplets at the transition temperatyre 
of -39°C is of primary importance in the formation of cirrus crystals. ) 

Langmuir, analyzing the behavior of cumulus clouds, described an 
action which he called cirrus-pumping. This occurs when, with few or no 
nuclei present, the cloud rises to great heights. If it rises to a height when 
the temperature gets down to -39°C or thereabouts, minute ice crystals are 
formed in great numbers, almost instantaneously. These come into contact 
with the supercooled water droplets in the cloud and immediately cause them 
to freeze. This, in turn, liberates a large amount of heat simultaneously over 
the whole top of the cloud, and this upper part rises still further, forming a 
cirrus crown shaped something like a pancake. 

The pancake grows in dimension and gets thinner, and it sometimes drifts 
gradually off to one side, so that it assumes the general appearance of an 
anvil--a type of cloud characteristic of the tropics. One large cloud of this 
type, said Langmuir, might sometimes produce cirrus clouds which would 
spread over 10,000 square miles. Outside of the tropics, they may often occur 
Sune ay summer in semi-arid regions such as New Mexico, Arizona, or 

Height, Temperature, etc. Some observations were made by the project 
of the height of cirrus clouds and their temperatures. 


Much more attention was paid to stratus clouds. The flight test of 
December 20, 1946, for example, was cen ucted when the sky was com- 
pletely overcast, and it produced snow. 12) Im the flight test of March 6, 
1947, now under the auspices of Project Cirrus, seeding was conducted 
on stratus clouds. Looking down on the cloud, it was observed, first, that 
a deep groove had been produced along the top of the seeded area, and snow 
fell. Soon the sky cleared up in a spectacular fashion, so that there was a 
cloudless area 20 miles long and 5 miles wide where the seeding had taken 
ee ey there were no other breaks in the overcast in any direc- 
tion, Further tests on stratus clouds produced similar results. 

Cirrus and Stratus Studies =e 

The conclusion was therefore reached in the earliest days of the pro- 
ject that cloud seeding could produce holes in stratus clouds. Thus a plane 
should be able to clear a hole for itself. The result would be not only to 
increase visibility but also to eliminate icing conditions. 

Langmuir made an exhaustive analysis of the photographic data ob- 
tained on these early test flights, reaching some very ete conclu- 
sions regarding the nature and behavior of stratus clouds. lg 

It was soon found that a very useful technique in seeding stratus 
clouds was to seed in patterns--L shapes, race-track shapes, Greek gam- 
mas, etc. Thus it would be possible to watch for modification'of the clouds 
following the same pattern. And invariably modification did occur, agreeing 
with the pattern of the seeding. In many cases clear areas were produced 
in the cloud deck. 

Among the stratus cloud studies made by the project were: 

(1) The effect of seeding supercooled stratus clouds with 
various amounts of dry ice and silver iodide. 

(2) The optimum quantity of seeding agent required to pro- 
duce large cleared areas in an otherwise solid deck of 
supercooled clouds. 


The most spectacular, fruitful, and controversial results produced 
by the activities of the project were those produced as a result of the work 
on cumulus clouds. This work, which started in the earliest days of the 
project, continued throughout its duration and let into some very inter- 
esting other activities. 

Flight tests on November 23 and 29, 1946, were made on isolated 
cumulus-type clouds. The whole of each cloud was changed into ice 
within five eee after seeding, and snow began falling from the base 
of the cloud.\7°) But it was realized that experiments with small cum- 
ulus clouds were of little interest, for the effects lasted but a few minutes. 
Other experiments were conducted with cumulus clouds in the early days 
of the project and, although many of them were changed to snow, the re- 
sults were of comparatively little interest. 

By the summer of 1947, however, some spectacular results were 
obtained with cumulus clouds, especially with thunderstorms. ‘These were 
so impressive that it was decided to make some studies of cumulus clouds 
and thunderstorms in New York State’s Sacandaga Reservoir territory, not 
far from Schenectady. 

This reservoir is situated just south of the southeast corner of the 
Adirondack Mountains. Evidence pointed to the probability that this large 
body of shallow water provides the moisture which feeds thunderstorms in 
eastern New York State. It was believed that the unusual conditions there 
could be used to observe the effect of seeding the intense thunderstorms 
developed. Actually, however, no seeding was performed there, although 
many photographs were taken and considerable time was spent in a study 
of conditions in that area. 


In 1948 and 1949, Langmuir visited Honduras, Guatemala, and Costa 
Rica to study tropical cloud formations, and particularly to learn what was 
being done by Joe Silverthorne, a commercial cloud seeder, in seeding 
clouds for the United Fruit Company. The work was being conducted for 
the purpose of testing out the possibility of controlling rainfall, and partic- 
ularly in the hope of stopping blow-downs that result from winds associated 
with thunderstorms, which occasionally destroy large stands of fruit trees. 

At Langmuir’s suggestion, Silverthorne tried out a number of ex- 
periments early in 1949 and made many worthwhile observations. It was 
Sometimes desired to produce rain, and sometimes it was desired to pre- 
vent rain. On the one hand, by overseeding the top of a high cumulus 
cloud, rain would be prevented. The top of the cloud would float off into 
_a higher altitude, where it would be blown away by the counter trade wind. 

Cumulus Studies -40- 

If, on the other hand, the cloud was seeded just above the freezing level, 
heavy rain might be produced. Similarly, water seeding by means of water - 
filled balloons released from airplanes might dissipate a cloud and produce 
rain at low altitudes, but it seemed that in such instances dry-ice seeding 
would be much more effective. 

April 18, 1949. The results of the flight on this day, with Langmuir 
seco qpanying Silverthorne aloft, were so outstanding as to merit detailed 
comment. The following is extracted from an account of the flight by 
Langmuir in the Project Cirrus report to the government of July 30, 1951: 

‘‘We flew up to Point Sal and found a mass of dry air above 
the moist air coming from the sea at an altitude of about 6000 
or 7000 feet....From a height of about 8000 feet, looking South, 
a whole panorama of high cumulus clouds could be seen rising 
above the smoke, which extended up to about 11,000 or 12,000 
feet further inland, although it was much lower than this near 
the sea. 

*‘A large cloud was found which rose, I believe, to a height 
of about 25,000 feet, and we seeded it by making a series of short 
passes into the cloud at an altitude of approximately 21,000 feet-- 
two pellets* about one inch cubed being dropped into the cloud 
at 50-second intervals during these passes. The whole circuit 
of the cloud was made, and then the plane moved off a short 
distance, enabling us to see the effect produced. 

‘‘A band around the cloud, perhaps 500 or 1000 feet high, 
was observed which obviously consisted of ice crystals and 
which ultimately detached itself from the lower part of the 
cloud and floated off as a huge mass of ice crystals that could 
be seen for a long time. 

‘‘After the top of this cloud had turned to ice crystals 
and had detached itself, there was left under this cloud 
nothing but a group of lower clouds that reached only about 
14,000 feet, which-was below the freezing level. Later we 
flew down among these clouds and found that cloud bases 
had gone down from 12,000 feet to about 7,000 feet. It was 
difficult to see whether any rain was falling because of the 
smoke, but from the lowering of the cloud base we concluded 

Se Nr eee ee en ee a ea ee ee ae 
*Dry ice. 

Cumulus Studies -41- 

‘that rain had fallen from the lower part, while the top 
of the cloud had detached itself and floated off towards 
the northeast. 

‘Shortly after seeding this cloud with 10 to 12 pellets, 
we picked out a smaller cloud nearby whose top reached 
about 20,000 feet and dropped one single pellet of dry ice 
one inch cubed on this cloud. About 8 or 10 minutes later 
we found that this whole cloud had changed to ice crystals. 
We flew through the ice crystal cloud and verified the fact 
that they were entirely ice crystals. You could see them 
blowing into the cabin, and we also found that the cloud grad- 
ually dissipated. It probably rained out from the lower part 
of the cloud but this was down in the smoke level where we 
could not see it, and the top of the cloud then gradually mixed 
with the surrounding dry air which had been deprived of its 
source of supply of moisture from below. 

‘In other words, on this day we had beautiful examples of 
two effects that can be produced by seeding with pellets of 
dry ice. First the seeding of the top of the cloud can cause 
the top to float off from the lower part. However, in this 
ease some of the ice crystals reach the lower part of the cloud 
and cause rain to dissipate it. In the other seeded cloud, 
which was much lower and reached only a few thousand feet 
above the freezing level, the whole cloud rapidly dissipated 
as the upper part changed to ice and the lower part rained out.”’ 

The results of the flight of April 18 constituted for Langmuir a won- 
derful demonstration of the effectiveness of single pellets of for 
modifying large cumulus clouds. Such single-pellet seeding had a number 
of practical advantages. 

It quickly became obvious to Langmuir that the set-up for carrying 
out cloud-seeding experiments in Honduras was unique. Silverthorne made 
flights virtually every day, and, somewhere within a 150-mile range, clouds 
were nearly always found suitable for seeding. Such clouds were almost 
always orographic and associated with certain mountains. 

Many interesting experiments were conducted, and almost always 
the clouds could be profoundly modified with single pellets of dry ice. 
The latter part of Silverthorne’s seeding operations used 10-20 peNets, 
presumably to make sure the crystals were more uniformly distributed. 

Cumulus Studies -42- 


Meanwhile the study of cumulus clouds had been approached from an- 
other angle. Early in 1948 a visit was paid to the Research Laboratory and 
Project Cirrus by H. T. Gisborne of the Northern Rocky Mountain Forest 
and Range Experiment Station, United States Forest Service. Gisborne was 
in charge of fire research for Region No. 1. He wanted to learn more about 
cloud modification studies. 

This fitted in nicely with Schaefer’s interest in the same subject. He 
was anxious to study thunderstorms in a good breeding ground, and Gisborne 
wanted to see if anything could. be done to reduce forest fires by thunderstorm 

As a result, Schaefer visited the Laboratory at Priest River, Idaho, in 
July of that year (1948). He conducted quite a study of conditions there and 
made rather complete recommendations for a plan of future activity--a plan 
_ which should produce beneficial results from both Gsnepomts: Gisborne’s 
practical aspects and Schaefer’s theoretical ones. 

Actually, the recommendations were never put into effect. A consid- 
erable force for the completion of the project disappeared with the death of 
Gisborne. Although the project is still incomplete, interest still exists, how- 
ever, both at Schenectady and at Priest River. 


Further data, supplied from still another source, had some unexpected 
and very interesting implications and results. 

Early in 1947 a request for information on techniques of dry-ice seeding 
was received from the Pineapple Research Institute of Honolulu, Hawaii. This 
information was supplied by the Research Group of Project Cirrus, which had 
been supplying similar information to meet numerous requests Since the pub- 
lished reports appeared of Schaefer’s historic snowmaking flight over Pitts - 
field in 1946. But in this case there was an unexpected aftermath. 

In October, Honolulu newspaper accounts were received in Schenectady, 
describing experiments carried out over the island of Molokai by Dr. L. B. 
Leopold and Maurice Halstead of the Pineapple Research Institute. A few 
weeks later, copies of a preliminary report were received from these two 
men, describing interesting results obtained by dumping dry ice into cumulus 
clouds having temperatures above the freezing point. 

Results in Hawaii -43 - 

This was an important development. Although Langmuir had given 
some thought to the effects of seeding nonsupercooled clouds, he hadn’t 
done much about it, and this new work caused him to restudy theoretical 
calculations bg had prepared in 1944 in connection with the work at Mt. 
Washington. | ) 

He now had a new approach to the subject of weather modification: 
the growth of rain. 


The result was Langmuir’s chain-reaction theory of rain production, 
in brief, as follows: A typical large drop of water grows in size as it falls 
through the cloud, growing faster and faster until it gets so big that it 
breaks up, producing smaller droplets. If there are rising air currents, 
the little droplets will be borne aloft into the cloud again, growing in size 
as they go, until they get so big that they start falling again. This process 
continues in a chain reaction, causing the whole cloud to go over into heavy 
rain. Under the right circumstances, according to this theory, seeding 
with water would be just as good as with dry ice. 

The outgrowth of this, in turn, was considerable work by Project 
Cirrus to test Langmuir’s theory and apply some of its principles in prac- 
tice. For example, to determine the validity of several of the important 
phenomena which his theory postulated, laboratory studies were initiated 
of the erpyye of water droplets and of the behavior of droplets floating in 
the air.’’~’ These studies continued for a considerable period in the 
laboratory, and some very interesting observations were made and data 
collected. Later, the Research Group did considerable work in the stud 
of the drop size and size distribution of various types of precipitation. 3 

As another approach to the subject, an extensive series of exper- 
iments was conducted to explore the possibility of inducing precipitation 
or other modification in growing cumulus clouds by water seeding. 

The complete exposition of the theory by Langmuir was a beautiful 
example of theoretical analysis and mathematical calculation.(13) Among 
other things, it reviewed the knowledge of cloud physics which had al- 
ready been gained in the light of the new theory, summing up the probable 
behavior of both stratus and cumulus clouds. It went so far as to suggest 
that the chain reaction could, under the right conditions, be started by 
introdicing even a single drop of water into a cloud, although the action 
would be most rapid when many large drops were introduced near the 
top of the cloud. It outlined the probable behavior of self-propagating 
storms. It postulated that the phenomena that occur in artificial seeding 

Cumulus Studies =44— 

with dry ice or with water are essentially no different from those that occur 
spontaneously in nature. ‘‘However,’’ it went on, ‘‘there will frequently be 
cases where the cloud is not yet ready or ripe for spontaneous development 
of snow or rain, although it may be possible to produce these effects by 
seeding.’’ It concluded with the following significant summary: 

‘‘When we realize that it is possible to produce self- 
propagating rain or snow storms by artificial nucleation 
and that similar effects can be produced spontaneously by 
chain reactions that begin at particular but unpredictable 
times and places, it becomes apparent that important 
changes in the whole weather map can be brought about 
by events which are not at present being considered by 
meteorologists. I think we must recognize that it will 
probably forever be impossible to forecast with any great 
accuracy weather phenomena that may have beginnings 
in such spontaneously generated chain reactions.’’ 


All these studies and tests which had been made, and theories which 
had been evolved as a result, with regard to the nature, behavior, and modi- 
fication of cumulus clouds were an important background to another signif- 
icant milestone in the history of P pect Cirrus, That was the expedition 
to Puerto Rico in February, 1949. 4 

The objective of this trip was mainly to determine the type and physical 
characteristics of the clouds that occur in Puerto Rico during the winter 
months, particularly the month of February, and, if suitable clouds were en- 
countered, to develop and possibly to evaluate water-seeding techniques. Con- 
Siderable personnel took part in the project, a supply of planes was available, 
and a large quantity of photographs was made. 

At least two new precipitation sequences were observed, and considerable 
data were accumulated to permit a better understanding of the processes in- 
volved. Also studied was the trade wind inversion, a dominant feature which 
controls cloud and precipitation development in the West Indies region during 
February. A better understanding of this phenomenon should lead to a better 
understanding of tropical meteorology. 

The cumulus clouds were observed to have a different character than 
those common in the eastern United States. Contacts made with interested 
local people in Puerto Rico were expected to lead to the accumulation of 
some excellent supplementary data on raindrop size, convergence of winds, 
and the observation of double orographic cloud streams from the Liquillo 

Cumulus Studies AG 

The carrying out of successful ground-air operations on three dif- 
ferent occasions, using lapse-time photographs as part of the ground 
coverage, demonstrated conclusively to the members of the project the 
value of carrying out such studies of clouds which develop in definite 
cloud-breeding regions. Similar areas in the United States known to 
possess such developments were Albuquerque, New Mexico, and Priest 
River, Idaho. Schaefer had already visited Priest River, and arrange- 
ments had been made for investigations and experiments there. And 
a test mission had been conducted at Albuquerque the previous year, 
details of which will be found in the next section of this report. (See 
last paragraph on this page.) 

Despite the fact that no suitable clouds were found for testing out 
water-seeding techniques during the period, many valuable results were 
obtained which it was expected would lead to a much better understanding 
of the formation of rain in tropical clouds. 

One of the very important results of the expedition was the obser- 
vation of the important effect of salt nuclei on the formation of precipi- 
tation in thin tropical clouds. Said one of the reports: ‘“‘This seems, 
on first sight, to be of great importance in explaining the rain showers 
which are of daily occurrence and random distribution in the vicinity of 
Puerto Rico. Rarely is rain observed from such clouds in the eastern 
United States.’’ Said Langmuir: 

‘‘Observations in Puerto Rico in 1949 and in the Hawaiian 
Islands in 1951 have shown that the rainfall depends on rela- 
‘tively large particles of sea salt in the air, in accord with the 
publications of A. H. Woodcock and Mary Gifford. Calcula- 
tions of the rate of growth of salt particles indicate that it 
should frequently be possible to induce heavy rainfall by 
introducing salt into the trade wind at the rate of about one 
tone per hour in the form of fine dust particles of about 25 
microns in diameter. The heat generated by the condensation 
may liberate So much heat as to produce profound changes 
in the air flow and the synoptic conditions in neighboring 


Although interest in cumulus clouds and thunderstorms was high 
among the members of the Research Group in 1948, the cumulus season 
passed in the vicinity of Schenectady without any significant flights 
having been carried out. It was realized that the best results could be 
obtained from the seeding of cumulus clouds in a region where storms 

‘Cumulus Studies SANG} — 

originate, rather than in a region which, like the Schenectady area, is 
traversed by storms. Chairman Stine of the Operations Committee had 

had experience as a forecaster in New Mexico, and he strongly recommended 
that that region be used as a base for experiments with cumulus clouds. This 
recommendation was seconded by Schaefer, who knew of the work being done 
in this field by Dr. E. J. Workman’s group at the New Mexico School of Mines 
and who had obtained a promise of co-operation from Workman. 

Accordingly, it was decided to attempt a flight to Albuquerque, New 
Mexico, to determine whether the radar and other facilities of Dr. Workman’s 
group would be of assistance in this respect. In view of the waning cumulus 
season even at that location, preparations were made to carry out full-scale 
tests if proper clouds were formed. 

As a result, members of the project spent three days at Albuquerque 
during mid-October of 1948. A working arrangement was quickly made with 
Dr. Workman and his staff for radar tracking and photography of the tests 
to be made. Two seeding flights were made, one on October 12 and the 
other on October 14. The second of these two flights was performed under 
such satisfactory conditions that the results obtained were considered partic- 
ularly significant. 

For example, an exceptionally complete aerial photographic record was 
made of the conditions of the cloud that was seeded from one of the planes, 
including 176 photographs 4'' x 5", plus pictures taken every 45 seconds of a 
group of instruments giving time, altitude, air speed, heading of the plane, and 
other pertinent information. Every time a photograph was taken of the cloud, 
another picture would be taken of a clock and other instruments, thus recording 
when the photograph was taken amlother significant data. In this way an in- 
valuable flight record was made of the test. 

Further data were collected on the ground. Lapse-time movies were 
made of the clouds as seen from the station, as well as a series of still 
pictures, and radar was used to detect any rain that might fall. Although 
some excellent supporting data were thus obtained, unfortunately it was not 
as complete as it might be because of a failure of the radio communication 
between the airplane and the radar station. But significant radar observa- 
tions were made, and photographs were taken of the radar scope, giving a 
complete set of records of radar observations for a considerable period 
of time, 

Four seeding operations were conducted on the October 14 flight. The 
details of these seedings and the results obtained were discussed at consid- 
erable length by Langmuir in an occasional report, (20) But a summary of 
his findings is to the effect that rainfall was produced over an area of more 

Cumulus Studies EAs 

than 40,000 square miles as a result of the seeding--about a quarter of 
the area of the State of New Mexico. And substantially all of the rain for 
the whole of New Mexico that fell on October 14 and 15 was the result of 
the seeding operations near Albuquerque on October 14. ‘“The odds in 
favor of this conclusion as compared to the assumption that the rain was 
due to natural causes are many millions to one.’’ 

An early estimate by Langmuir was that about 100,000,000 tons of 
rainfall was produced. Later, using the rain reports from 3380 stations 
given ina U.S. Weather Bureau publication, he concluded that the orig- 
inal estimate was unduly conservative. 20) Said he: ‘“The evidence in- 
dicated that the rain started from near the point of seeding shortly after 
the time of seeding and then spread gradually at a rate which at no place 
exceeded 22 miles per hour, over an area of at least 12,000 square miles 
north to northeast of Albuquerque with an average of about 0.35 inches. 
This corresponded to about 300,000,000 tons.’’ 


So satisfactory were the tests conducted at Albuquerque in 1948 that 
it was decided to make a further study of cumulus clouds at that location 
in the middle of July the following year. Much more elaborate plans were 
made for this second expedition; for example, not one but a number of 
airplanes took part, and virtually all the members of the Research and 
Operations Groups went along. 

Previous to the arrival of the main body of the project, Langmuir 
and Schaefer investigated the general cloud situation in the various moun- 
tain regions nearby and decided the cloud systems along the Rio Grande 
Valley near Albuquerque were superior for their purpose to anything 
they could find in other parts of Arizona and New Mexico. In addition, 
the excellent radar, photographic, and shop facilities of the Experimental 
Range of the New Mexico School of Mines appeared to be ideal for carrying 
out the operations planned. 

Between July 13 and July 22 a total of ten flights was conducted, on 
eight of which two or three planes participated. Excellent co-operation 
was enjoyed in every phase of the operation, and an extensive mass of 
data was obtained both in the air and at the ground stations which were 
set up. Seeding operations with varying amounts of dry ice and the 
ground eee of a Silver-iodide generator were the subjects for the 
flight studies (18 

Again the dry-ice seeding was successful, and the results of the 
various airborne seeding operations was quite satisfactory. But a new 
factor was introduced into this second expedition which put an entirely 

Cumulus Studies =43= 

different aspect upon the results and had a tremendous influence on the 
course of future investigations and analysis. This was the effect of ground 
seeding with silver iodide. 

As usual, close attention was paid to changes in weather conditions, in 
order to obServe any correlation between such changes and the dry-ice seeding. 
But, although Vonnegut was conducting some silver-iodide seeding on the 
ground, this was disregarded by Langmuir, who was concentrating on the air- 
borne dry-ice seedings. Consequently, when he noticed some weather conditions 
which could not be explained by the airborne seeding, he was puzzled. 

Then he suddenly became conscious of the fact that Vonnegut had been 
trying to call the ground seeding of silver iodide to this attention, and he im- 
mediately realized that this might explain the discrepancies he had observed. 
Further study convinced him that this was, indeed, the case. 

Not only that, but the results of the seeding activities in New Mexico the 
preceding year were reconsidered in the light of this development. And it 
appeared reasonable to conclude that the similar widespread effects produced » 
in October, 1948, were the result of the silver-iodide seeding which was done 
at that time, rather than of the dry-ice seeding, which had been the previous 

Langmuir made, as was his habit, an exhaustive analysis of the available 
data and presented a striking summary of his findings 18) from which the fol- 
lowing is quoted: 

“I wish particularly in this paper to describe the more wide- 
spread effects that were produced by the operation of the silver- 
iodide generator on the ground during July, 1949, near Albuquerque. 
The first seeding with silver iodide during this stay in New 
Mexico was on July 15, 1949, but the generator was not run for 
more than a couple of hours on each day thereafter until the 19th, 
when it was operated for a short time only, late in the afternoon. 
On July 20 it was not operated at all, but on the 21st it was op- 
erated for 13 hours, starting about 5:30 a.m. and using 300 
grams, or a total of 2/3 pound of silver iodide. 

‘*Tests made by Dr. Vonnegut have shown that each gram of 
silver iodide dispersed under these conditions produced 107° 
sublimation nuclei that are slowly effective at -5°C but very 
rapidly effective at -10°C. 

Cumulus. Studies -49 - 

‘‘The new probability theory....has served a valuable guide 
in devising an objective method of evaluating the distribution 
in space and time of the rain which follows the operation of 
the silver-iodide generator on the ground or in the airplane 
flights near Albuquerque. To illustrate the results, we will an- 
alyze the data obtained on two days, October 14, 1948 (Flight 
45) and July 21, 1949 (Flight 110). 

‘These days were chosen because large amounts of sil- 
ver iodiue were used, but no seeding was done on the imme- 
diately preceding days. Furthermore, the wind direction on 
both days was rather similar. On both days the Weather 
Bureau predicted no substantial amount of rain. Both morn- 
ings were nearly cloudless, and on both days SW winds pre- 
vailed from the cloud bases at 12,000 feet up to 20,000 feet. 
At lower and higher altitudes and later in the day there were 
also winds from the E, W, and NW. On both days, visual 
effects indicating thunderstorms and heavy rain over wide 
areas were observed a few hours after the start of the seeding 

‘In the July operation our techniques had been improved 
compared to those of the preceding October. In October ra- 
dar observations covered only a period of about an hour in 
the afternoon, for at that ime it was not suspected that the 
rain that lasted well on to the morning of the 15th had any- 
thing to do with the seeding. 

*‘On July 21, 1949, however, we had complete radar cover- 
age from early in the morning until late at night. Photographs 
of the clouds were taken not only from planes but from the 
ground, including lapse-time motion pictures with photographs 
every few seconds. ; 

‘Shortly before 8:30 a.m. on July 21, 1949, a single large 
cumulus cloud began to form about 25 miles S of the field sta- 
tion near Albuquerque in a sky that was otherwise cloudless. 
This cloud was located near the Manzano Mountains, and the 
silver-iodide smoke had been blowing from the N about 10 mph 
so that it should have reached the position of the cloud. 

‘‘Between 8:30 and 9:57 the cloud grew in height slowly at 
the uniform rate of 160 feet per minute. At 9:57, when the top 
of the cloud was at 26,000 feet (temperature -23°C), the upward 
velocity of the top of the cloud increased quite suddenly, so that 
the cloud rose 1200 feet per minute until at 10:12 it had reached 
44,000 feet (temperature -65°C). 

Cumulus Studies L'5(0)= 

_ **At10:06, when the top of the clowl was 36,000 feet (temperature 
-49°C), the first radar echo return was obtained from the cloud 
at an altitude of 20,500 feet (temperature -9°C). The distance 
given by radar was 25 miles at an azimuth of 165°, which was 
exactly where the cloud was found to be from visual observations. 
The area p precipitation in the cloud was about one square mile 
at that time and was deep within the mass of the cloud. Within 
four minutes, the precipitation area had increased to seven 
Square miles, and within six minutes after the first echo ap- 
peared, the precipitation had extended upward to 34,000 feet, 
where the temperature was -43°C. 

“The chain reaction in this cloud started at low altitude at 
a time and place which agreed well with the trajectory of the 
silver -iodide smoke. 

‘*The first flash of lightning was seen at 10:10, four minutes 
after the first radar echo was detected. In all, perhaps a dozen 
flashes of lightning formed from this cloud, and very heavy rain 
was seen to fall to the ground. Ihe top of the cloud moved to- 
wards the W, but the lower part of the cloud, from which the 
rain was falling, moved gradually to the NE. 

*‘At 10:45, a second cloud about eight miles still further 
to the NE developed a radar echo, and from that time on during 
the day there was an increasing number of rainstorms giving 
very heavy showers in the neighborhood. During the late after- 
noon 1.2 inches of rain fell at the station where the generator 
was located. The phenomena observed near and at Albuquerque 
from the ground and the radio reports of exceptionally heavy 
rain at Santa Fegave immediate evidence of the success of this 
operation in producing heavy rain.’’ 

Langmuir’s report then analyzes river flow data and rain gauge data 
for the region. In discussing the rain gauge data, he says: 

‘The Weather Bureau observer with Project Cirrus in 
New Mexico stated that he considered it possible or even prob- 
able that seeding operations carried on there could have in- 
creased the naturally occurring rain by five per cent, but certainly 
not more than 10 per cent. If this were ture, it would be possible 
to conclude that seeding operations have economic value only if 
experiments are carried on many hundred of days, and a statis- 
tical analysis is made of the rainfall data for all of these oper- 

Cumulus Studies ails 

‘*The rainfall data actually show, however, that the rainfall 
on both October 14, 1948 and July 21, 1949 was exceptionally 
high and could not have possibly been accounted for as the re- 
sult of naturally occurring rain. This proof is made by the 
analysis described in this paper. 

‘‘The map of the State of New Mexico, which represents 
about 120,000 square miles, was divided into eight octants or 
45° sectors radiating out from Albuquerque. Then concentric 
circles having radii of 30, 75, and 125 and 175 miles were 
drawn on the map. This divided the whold state into 27 regions 
whose average distances and directions from Albuquerque were 

‘‘By entering on the map for each of these regions the 
average rainfall for Flights 45 and 110, a comparison could be 
made of the distribution of the rain on those two days. An ob- 
jective way of evaluating the similarity between such two dis- 
tributions is to employ the statistical device known as the 
correlation co-efficient. This was found in this case to be 
+0.78+ 0.076. The chance that such a high value would occur 
among these figures if one set of them were shuffled giving 
a random distribution is only 1 in 10. Such close agreement 
in the distribution on two days could thus hardly be the result 
of chance. There must be an underlying cause. 

‘“We believe that the close similarity in distribution is 
dependent not only on the rather uniform synoptic situations 
over the states that prevailed on these days, but also depended 
on the fact that on both days the probability of rainfall depended 
on the nuclei that spread radially out from Albuquerque, the 
concentration decreasing as the distance from Albuquerque in- 

‘*The next step was to investigate just what characteristics 
of this distribution were so similar on these two days. On each 
of the two days, nearly all of the rain that fell occurred within 
four of the eight octants. If each sector were divided into four 
to six parts arranged radially so that each would contain equal 
numbers of observing stations (about eight per region), the an- 
alysis showed that the average rainfall rose rapidly to a max- 
imum in intensity about 30 miles from the point of seeding and 
that in each of the four sectors it decreased regularly as the 
distance from the source of the silver-iodide smoke increased. 

Cumulus Studies 5h 

‘In fact, this decrease followed quite accurately equations (2) 
and (3), which indicated that the rain fall depended on the con- 
centration of nuclei, and this, in turn, varied inversely in pro- 
portion to the distance from the source. 

‘‘This analysis makes it possible to separate the effects 
of the artificial silver-iodide nuclei from that of the background 
of sublimation nuclei that were already present in the atmosphere. 
The analysis gave proof that C, = 0, so that there was no appreci- 
able background on each of these two days. We must conclude 
that nearly all of the rainfall that occurred on October 14, 1948 
and July 21, 1949 was the result of seeding. 

‘*The agreements between the intensity of the average rain- 
fall in separate regions and the theoretical equations were So 
good in each of the four sectors on October 14 and July 21 that 
the probability factors for each sector ranged from 102 to 10%. 
Taking all the octants together, the probability factor rose to ; 
about 10 &to.l. 4 

‘*For each of the eight octants that gave appreciable rain, 
the rain started progressively later as the distance from the 
source of the silver iodide increased. The advancing edge of 
the rain area thus moved from Albuquerque on July 2l ata 
velocity of about 15 mph and on October 25 at a speed of about 
25 mph. These velocities agree well with the wind velocities 
observed at various altitudes. 

**The method of correlation coefficient can be applied to 
the relation of the time of the start of the rain to the distance 
from Albuquerque. This indicates that there is another prob- 
ability factor which is the order of 108to l. 

‘“Taking these results altogether, it seems to me we may 
say that the results have proved conclusively that silver -iodide 
seeding produced practically all of the rain in the State of New 
Mexico on both of these days. 

‘‘T have not mentioned what happened on the other days. 
The results, although somewhat more complicated due to the 
overlapping of the effect of seeding on successive days, are 
almost as striking as those of Flights 45 and 110, in which we 
used silver-iodide seeding. Very high probability factors are 
found, which help confirm the results indicated by the analysis 
of Flights 45 and 110. 

Cumulus Studies = a= 

‘*The total amounts of rain that fell in the state on the 
two days as a result of seeding were found to be 800 million 
tons on October 14, 1948 and 1600 million tons on July 21, 1949. 
If these units are not so familiar to you, 1 may say that on 
October 14, 1948, the total amount of rain resulting from seed- 
ing was 160 billion gallons and on July 21, 1949, 320 billion 

‘Dr, Vonnegut has measured the number of effective sub- 
limation nuclei produced by the type of silver-iodide smoke 
generator used in our New Mexico experiments for each gram 
of silver iodide used....One thus finds that, to get a 30-percent 
chance of rain per day within a given area in New Mexico, the 
cost of the silver iodide is only $1. for 4000 square miles. 

‘If similar conditions prevailed over the whole United 
States, the cost per day to double the rainfall would be only 
of the order of a couple of hundred dollars. This verified an 
estimate that I made in November, 1947 in an address before 
the National Academy of Sciences that ‘a few pounds of silver 
iodide would be enough to nucleate all the air of the United 
States at one time, so that it would contain one particle per 
cubic inch, which is far more than the number of ice nuclei 
which occur normally under natural conditions.’ Such a dis- 
tribution of silver-iodide nuclei ‘in the atmosphere might 
perhaps have a profound effect upon the climate.’ ”’ 

The report then discusses a new theory which Langmuir had devel- 
oped of the rate of growth of snow crystals in supercooled clouds contain- 
ing known numbers of sublimation nuclei. After a brief exposition of the 
basis of this theory, he says: 

‘From the probability theory of the growth of showers 
from artificial nucleation, one obtains the result that the 
total amount of rain produced by operating a ground generator 
increases in proportion to the square of the amount of silver 
iodide used. Thus, with three times as much silver iodide 
one would get nine times the rainfall. The intensities of the 
showers would be no greater, but they would extend over a 
greater area. 

‘An analysis of the July 1949 rainfall in New Mexico, 
Arizona, Colorado, Oklahoma, Kansas, and Texas gives evidence 
that a band of heavy rain progressed in an easterly direction 
during the period of July 20 to July 23 from southern Colorado 
across the southern half of Kansas, where it gave 3 to 5 inches 

Cumulus Studies ~54- 

‘of rainfall in many places. It may have been dependent on the 
silver-iodide nuclei generated near Albuquerque between July 
18 and 21 and in central Arizona between July 19 and 21. 

‘‘Furthermore, the heavy rains that spread throughout New 
Mexico from July 9 to 13 before the start of Project Cirrus 
seeding experiments appear to have depended on silver-iodide 
seedings in Arizona on July 5 and 6. 

‘Tt is very important that regular tests on certain selected 
days of each week be carried out throughout the year, using 
amounts of seeding agents just sufficient to obtain conclusive 
statistical data as to their effectiveness in producing widespread 
rain. It is to be expected that the results will vary greatly in 
different parts of the country, because of the changes in synoptic 

The significance of the two test projects at New Mexico is thus apparent. 
They indicated not only the possibilities of silver-iodide seeding from the ground, 
but they suggested a widespread effect on the weather of the nation. And, asa 
result, the project conducted some experiments in periodic seeding which were 
destined to have a profound--and controversial--significance. 



By this time, a rather close liaison had been established with Dr. 
Workman and his co-workers at the New Mexico School of Mines. So, 
in view of the significance of Langmuir’s analysis of the effects and 
possibilities of silver-iodide ground seeding, and in order to test as 
soon as possible his ideas on periodic seeding, a schedule of operations 
on this basis was estiblished without further ado at New Mexico. 

Starting in December, 1949, a silver-iodide ground-based gener- 
ator was operated in New Mexico by the project on a schedule so planned 
as to introduce, if possible, a seven-day periodicity into the weather 
cycles of the nation. This schedule of regular weekly periodic seedings 
used about 1000 grams of silver iodide per week, and it continued with 
a few modifications until the middle of 1951. 

Data were gathered by Falconer, and almost immediately Langmuir 
found evidences of a definite weekly periodicity in rainfall in the Ohio 
River Basin. Again, he conducted an exhaustive analysis of the facts and 
performed elaborate mathematical calculations to determine the prob- 
abilities that these variations in weather could have taken place by pure 

He reported his findings and his conclusions to the National Academy 
of Sciences, October 12, 1950 to the American Meteorological Society of 
New York City on January 30, 1951 (25). and also to the New York Academy 
of Sciences on October 23, 1951.(24) He pointed out that, during 1950, 
there was a marked and statistically highly significant seven-day perio- 
dicity in many weather elements. The significance was So high, said he, 
that it could not be explained on the basis of chance; it could not have 
occurred anyway from natural causes. It involved not only rainfall but 
also pressure, humidities, cloudiness, and temperatures over much of 
the United States. 

In his paper to the New York Academy of Sciences, (24) Langmuir 

“‘Almost immediately, that is, during December 1949 and 
January 1950, it was noted that the rainfall in the Ohio River 
Basin began to show a definite weekly periodicity. A conven- 
ient way of measuring the degree of periodicity was to calcu- 

late the correlation coefficient CC between the rainfall on the 
successive days during a 28-day period, with the sine or the 
cosine of the time expressed as fractions of a week, the phase 
being taken to be O on Sundays. 

Periodic Seeding -06= 

‘Just before the start of the periodic seedings, the corre- 
lation coefficient CC(7) based on the seven average values for 
the successive days of the week of the 28-day period amounted 
to only 0.28, but in the next 28-day period the value of CC(7) 
rese-to,0 017 

*“Table I gives the average rainfall in inches per station 
day during 140 days at 20 stations designed as Group A in the 
Ohio Valley Basin, representative of an area of about 600,000 
Square miles, The successive rows correspond to five succes- 
Sive 28-day periods. It will be noted that the average rainfall 
on Monday was 0.272", whereas on Saturday it was only 0.064", 
a ratio of 4.3:1 The next to the last column gives CC(28), the 
periodic correlation coefficients for each 28-day period, and 
the last column gives the phases in the successive periods. 
Taking the 35 separate values for the 4-week averages given 
in the table, one gets CC(35) = 0.689 with a phase of 1.60 days. 
This result is statistically highly significant. 

*“These periodicities in rainfall were evident at almost 
any set of stations in the northeastern part of the United States. 
Table 2 gives the rainfall on successive Tuesdays and Saturdays 
during a 12-week period during the winter of 1949-1950 at Buffalo, 
Wilkes-Barre, and Philadelphia. This periodicity is almost the 
Same as that found in the Ohio River Basin but with a one-day 
phase lag. The striking contrast between the total rains on 
Tuesdays and Saturdays runs parallel to the total number of 
days on which rains of 0.1" or more occurred on Tuesdays and 
on Saturdays. 

‘‘Maps have been prepared giving for 24 successive 28-day 
periods the distribution of correlation coefficients, CC(28), 
among 17 subdivisions of the United States, these data being 
based on daily weather reports of 24-hour rainfall at 160 sta- 
tions. During the first five 28-day periods there were always 
several adjacent subdivisions that showed high weekly perio- 
dicities in rainfall. After May 1950, however, the periodicities 
became somewhat sporadic, although highly significant perio- 
dicities over large areas still occurred during more than half 
of the periods after July 1950. Presumably the large amount of 
commercial silver-iodide seeding in the western states (not done 
with a weekly periodicity) masks the effects of the periodic 
seedings in New Mexico. By a map, the areas were shown in 
which known seeding operations have been carried on in 1951. 


Periodic Seeding -57- 

‘In 15 states west of the 95° W meridian (excluding Texas) 
about 550,000 square miles of 37 per cent of the total area of 
these states were under Seeding contracts during 1951. 

‘‘Maps for the months from December 1949 through July 
1950, taken from the Monthly Weather Review, illustrated the 
distribution of abnormally large rainfalls over the United 
States. The heavy rains nearly always occurred in a band ex- 
tending from the southwestern to the northeastern states. 

*‘An analysis of the periodicity in the rainfall induced by 
periodic seeding was presented in a paper read October 12, 
1950 before the National Academy of Sciences. The areas 
having a high weekly periodicity were generally the same as 
those showing the highest abnormalities in rainfall. Such ~ 
heavy rains can only occur if the winds and the barometric 
pressures cause an adequate supply of moisture to flow from 
the Gulf of Mexico. The periodicities in the pressure differ- 
ences between Corpus Christi and Jacksonville were studied. 
During the first 140 days after seeding began, there was a 
highly significant weekly periodicity indicating a periodic air 
flow from the Gulf. 

‘The upper air temperatures, even up to the stratosphere, 
showed a high weekly periodicity over more than half of the 
United States. Nine stations representative of an area of 
1,300,000 square miles gave 950 mb temperatures having. CC(28) 
greater than 0.5. These data were published, in detail for 
Chicago and in summary for eight other stations, in the Dec- 
ember issue of “The Bulletin of the American Meteorological 
Society’, and a statistical analysis was given which proved that 
these periodicities were highly significant. Mr. William Lewis 
and Mr. E. Wahl, Bull.Amer.Met.Soc.32:192-3 (1951), and Mr. 
Harry Wexler, Chem.Eng. News 29:3933 (1951), maintained, 
however, that these data on the periodicities in temperature 
were not truly significant and similar weekly periodicities have 
frequently occurred in the past. 

‘The degree of periodicity in upper-air temperatures ob- 
served in 1950 during April, July, and November shows a stat- 
istical significance of a much higher order of magnitude than 
those referred to by Lewis, Wahl, and Wexler. To illustrate 
this, an analysis has been made of the temperatures at the 
700 mb level at nine stations in the United States at the inter- 
sections of the 80, 90, and 100° W meridians with the 35, 40, 
and 45° N parallels. 

Periodic Seeding -58- 

‘‘The value of CC(28) at these nine points of intersection 
ranged from 0.50 to 0.85. The area represented is 1.5 million 
Square miles. 

‘Recently we have extended this grid of regularly spaced 
stations to include the intersections of the 45° N parallel with 
the 70° W and 110° W meridians, these points giving CC values 
of 0.66 and 0.65 respectively. The 30° N, 80° W intersection 
just off Jacksonville, Florida, also gave a correlation of 0.65. 
We thus have an area of two million square miles or 2/3 of the 
area of the United States in which CC(28) exceeds 0.50 with a 
mean value of €G(28) = 0.67. 

‘‘We have also examined these periodicities at corresponding 
points for preceding and for following periods. The 28-day per- 
iod in May showed low correlations. On the other hand, the two 
preceding periods gave highly significant values. Apparently 
the high periodicity in the upper air temperatures started about 
January 25, 1950 and continued on until about May 1, 1950, covering 
an average area of about half of the United States. 

‘‘For the nine points of intersection during a 28-day period 
in April, 1950 the total variance of the temperature was deter- 
mined by taking the total sums of the squares of the deviations 
of these temperatures from their mean and dividing by 27, the 
number of degrees of freedom. The data obtained in this way 
are called the ‘total variance’. By multiplying these values for 
each of the nine stations by the corresponding square of the cor- 
relation coefficient CC(28), one obtains the ‘periodic component 
of the variance’, 

‘Exactly similar calculations were made for a 28-day period 
in April, 1949 when there was no periodic seeding. The results 
are given in Table 3. At each point the upper figure is the 
‘periodic component of variance’ for the April, 1950 period, 
and the lower figure is the corresponding value for April, 1949. 
The average values for all these nine points show that the 
‘periodic variance’ in 1950 was 18 times as great as in 1949. 

‘‘Table 4 gives the corresponding values of the ‘residual 
component of variance’ obtained by subtracting the ‘period vari- 
ance’ from the ‘total variance’. These data then indicate how 
all the other kinds of periodicities, beside the seven-day peri- 
odicity, compared with one another in the two years. It will be 
seen that there is only about 10 per cent difference between the 
average variance of this type for 1950 and 1949. 

Periodic Seeding -59- 

‘It seems, therefore, that the temperature fluctuations in 
1950 essentially differed from those in 1949 only in the super- 
imposition of an extremely high seven-day periodicity. 

‘Quite similar results have been obtained by detailed studies 
of the upper air temperatures in July, 1950 and November, 1950,”’ 

As indicated in this extract, Langmuir’s conclusions were contested 
by representatives of the United States Weather Bureau. Inasmuch as this 
controversy developed in considerable proportions, it is discussed in a 
later section of this report. (Page 77). 


In addition to the periodic seeding conducted in New Mexico, similar 
seeding was initiated in the Schoharie Valley, New York and at the base of 
Mt. Washington. An interesting result of the seeding at Mt. Washington was 
observed by Joseph B. Dodge, who has charge of the Appalachian Mountain 
Club lodges in the White Mountains for skiers and mountain climbers. Dodge, 
who knew nothing of the seeding, pointed out that, judging by the maps of snow 
coverage in Maine and New Hampshire, there were two bands of snow running 
at a diverging angle in the direction of those two states and coming to a point 
back at Mt. Washington. This was a season in which there was not much 
Snow, but along the line of these two bands there had been exceptionally heavy 
snow. The results of further study indicated that the lack of snow may have 
been caused by overseeding, but that along the two lines of heavy snow there 
had been just a light amount of seeding. 


Early in 1952, during the course of their normal analyses of weather 
conditions throughout the United States, Falconer and Maynard again found 
evidence of periodicity. Further study showed that the periodicity was on 
a seven-day basis and that it progressed regularly from west to east. The 
correlation coefficients were calculated by Maynard and found generally to 
be of a very high order. For one 28-day period the correlation coefficient 
was the highest so far obtained for the country as a whole. 

It was thought possible that this phenomenon might be caused by a 
corresponding periodicity in the commercial seeding going on in various 
parts of the West. Inasmuch as the periodicity in the weather progressed 
uniformly across the United States, it was possible to trace it ona map 
back to a likely point of origin. The commercial seeding organization 
active in that area was then asked by Schaefer for a schedule of its seed- 
ing operations, which it willingly furnished. It was found that the commer- 
cial seeding had a periodicity corresponding to that observed in the weather. 

Periodic Seeding -60- 

Langmuir, in analyzing the data thus obtained, observed that it would 
be difficult to determine cause and effect. In other words, it would be dif- 
ficult to know whether the periodicity in weather was caused by periodic 
seeding or vice versa. For commercial seeding organizations do not seed ~ 
at any random time but rather choose for seeding those days when weather 
conditions are propitious. If the conditions are ‘‘good’’ for the production 
of rain, the operator seeds. As a result, although it might rain naturally, 
the seeding may increase the quantity of rain--and it may produce rain 
when none would have fallen naturally. On the other hand, if conditions 
are not right for rain, the operator does not seed, for seeding will not pro- 
duce rain except when meteorological conditions are suitable. 

Meanwhile F. H. Hawkins, Jr., of the U.S. Weather Bureau, in the May 
1952 issue of the Monthly Weather Review, called attention to the same per- 
iodicity and stated that, as far as could be determined, no seeding which was 
under way that spring could compare in periodicity with the marked spacing 
of rainfall at that time. 

Langmuir, however, examined the data on western seeding operations 
and was able to show that the observed periodicity in weather conditions co- 
incided with the schedule of commercial operations. He reported his findings 
to this effect at the annual meeting of the Institute of Mathematical Statistics 
in East Lansing, Michigan, on September 4, 1952, 


In addition to the normal studies and tests with which Project Cirrus 
concerned itself, there were two additional activities in which it engaged 
early in its history. One was a study of tropical hurricanes and the other, 
an attempt to cause rain in a forest-fire area. Both took place in 1947. 


The hurricane study was planned by the various participating govern- 
ment agencies for the purpose of determining whether seeding operations 
could be carried out in such storms. These agencies hoped that the exper- 
idence thus gained would permit the planning of further operations in the 
future, with the hope of possibly steering or in other ways modifying trop- 
ical hurricanes. 

It was planned to study a ‘‘young’’ storm as Soon as possible after 
it had assumed the form of a hurricane. A group of General Electric per- 
Sonnel was requested to act as consultants on these operations by the 
chairman of the project’s Operations Committee. 

After a week of intensive organization and briefing, both groups were 
maintained in “‘stand-by’’ position, but the season progressed for some time 
without any suitable storms occurring. Finally on October 10, 1947 word was 
flashed from Miami, Florida, that a storm was forming below Swan Island 
in the Caribbean Sea. ae 

Plans were immediately activated, and the next evening the project’s 
two B-17’s were at Mobile, Alabama. The storm had traveled with such high 
speed, however, that by that time it was crossing Florida. The unit flew 
to MacDill Field, Florida the next day, joining forces with the 53rd Weather 
Reconnaissance group. Plans were laid for take-off early in the morning ” 
of October 13. The storm was expected to be from 300 to 400 miles east 
of Florida by that time. 

The following account of the observed features of the storm, the seed- 
‘ing operation, and observed effects was prepared by Lt.Com. Daniel F. Rex, 
at that time chairman of the Operations Group;(77) 

‘*The storm consisted of an eye approximately 30 miles 
in diameter, surrounded by a thick wall of clouds extending 
from about 800 feet up into the cirrus overcast at 20,000 feet 
and being some 30-50 miles thick radially. Several decks (4 
or 5) of stratified shelf clouds extended out from the outer wall, 
the upper-most deck having tops at 10,000 feet. These shelf 
clouds appeared as large areas (100-200 square miles) of solid, 
thin (1000-2000 feet thick) undercast, separated by large breaks 
through which the surface was often visible. An exceedingly 

Hurricanes and Forest Fires =O74= 

‘active Squall line, appearing as an almost continuous line of 
cumulonimbus with cirrus tops to an estimated 60,000 feet, 
was observed as a Spiral extending out from the center-base 
at 20,000 feet near the outer wall, lifting to 35,000 feet at the 

‘‘Approach to the storm center was effected from the south- 
west, this course bringing the group into the storm’s right rear 
quandrant. After a brief reconnaissance flight around the outer 
wall, the decision was made to seed a track over the uppermost 
cloud shelf and at a distance from the center sufficient to permit 
the control aircraft to fly contact 5000 feet above the seeding air- 

‘‘A formation intrail was used, with the seeding aircraft (B-17 
No. 5560) leading at cloud top level. The photoreconnaissance air- 
craft (B-17 No. 7746) followed the seed ship, 3000 feet above and 
1/2 mile astern, with the control aircraft (B-29 No. 816) trailing 
5000 feet above and 15-20 miles astern. 

‘Seeding commenced at 29.8 degrees North, 74.9 degrees 
West at 11:38 EST at an altitude of 19,200 feet, the outside air 
temperature being approximately -5°C. Continuous seeding was 
effected along a straight course to 30.2 degrees N, 73.9 degrees 
W, thence to 30.8 degrees N, 73.1 degrees W, at which point (12:08 
EST) seeding was stopped. During this 30-minute period 80 pounds 
of solid carbon dioxide was dispensed along the 110-mile track. 

In addition, two mass drops of 50 pounds each were made into a 
large cumulus top at 30.7 degrees N, 73.4 degrees W. 

“Upon completion of this phase, all planes flew a reverse 
course back along the seeded track, taking visual and photographic 
observations. No attempt was made to penetrate through the wall 
of the storm into the eye or to seed in or near the above-mentioned 
squall line, owing to the failure of the graip’s homing aids (radio, 
compass, and visual flares). It was thought that such an attempt, 
although desirable, would likely result in a separation of the air- 
craft, with subsequent abortion of the primary mission. 

‘‘Visual observation of the seeded area Showed a pronounced 
modification of the cloud deck seeded. No organized trough was 
observed; rather, the overcast previously observed appeared as 
an area of widely scattered snow clouds. The disturbed area cov- 
ered perhaps 300 square miles. No convective activity was seen 
to follow the seeding process at any time during the mission.’’ 

Hurricanes and Forest Fires =O5— 

In addition to this account by Rex, the following brief conclusions 
were prepared, after the test, by Schaefer, who carried on observations 
from the B-29:(79) 

**1, Many suitable clouds for seeding operations occur 
in this type of hurricane. 

‘<2. The seeding operation produced an area showing snow 
showers and stable snow clouds with light rain in the above-freezing 
region. The stable snow clouds covered considerable area and 
might have persisted long enough to affect other supercooled 
clouds. I concur with the estimate of Commander Rex that about 
300 square miles showed modification due to seeding operation. 

**3. The region where profound effects might have been pro- 
duced was in the extremely active squall line mentioned by Com- 
mander Rex. This was not attempted for the reasons indicated. 

*‘4. No build-ups were seen following the seeding operation. 
This was to be expected, owing to the thin character of the super- 
cooled clouds along the seeding path. 

**5. Owing to the complex structure of this ‘old’ storm, it 
is believed that a ‘young’ hurricane would provide much more 
satisfactory data for estimating the effect of seeding operations. 

**6, The operation pointed out the importance of making 
future studies a part of the hurricane reconnaissance program. 
Experimental seeding should be made by a group quite familiar 
with the structure of the particular storm, stationed in fairly 
close proximity, so that a number of forays would be made in 
rapid succession. 

*‘While the hurricane study project secured important in- 
formation and provided excellent training for the Project Cirrus 
personnel, the time required for planning such an operation and 
in analyzing the data raises the question of whether the results 
justify further activities of this kind by this particular group 
until the urgent and much simpler operations are completed 
at Schenectady.”’ 

Hurricanes and Forest Fires -64- 

Langmuir made some interesting observations with regard to the nature 
of the hurricane. (12) Speaking of the results of the seeding test, he said: 

‘‘The main thing that we learn from this flight is that we 
need to know enormously more than we do at present about hur- 

He concluded: 

‘Tt seems to me that next year’s program should be to 
study hurricanes away from land, maybe out considerably 
beyond Bermuda, out in the middle of the Atlantic....I think 
the chances are excellent that, with increased knowledge, I 
think we should be able to abolish the evil effects of these 


On October 29, 1947, a flight operation was carried out in Vermont and 
New Hampshire. At that time severe forest fires were raging uncontrolled 
in various parts of New England. Although it was not the policy of Project 
Cirrus to carry out such a widespread operation, it was felt that it would 
be worth the additional effort required to make such a flight for the exper- 
ience to be gained, particularly since it would be possible to use Schenectady 
as the base of operations. 

The flight was well planned from an operational point of view, but the re- 
sults were not spectacular, because of the absence over much of the area of 
suitable clouds--contrary to a forecast the previous day. Instead of encoun- 
tering a cloud deck at 18,000 feet as indicated by the forecast, the top of the 
stratus was about 10,000 feet, with isolated cumulus reaching a maximum of 
about 14,000 feet. 

Seeding operations were carried out by two B-17’s, the one normally 
in use by Project Cirrus and another furnished by Major Keating of Olmsted 
Field of the Signal Corps Weather Squadron. The site of operation was over 
some of the stratus near Montpelier, Vermont, and in the cumulus develop- 
ments. Practically all of the latter showed the effect of seeding after five 
to eight minutes. Subsequent reports indicated the development of some 
fairly intense local showers along the flight path. 

The next day word was received from Alan Bemis of the Massachusetts 
Institute of Technology Radar Research Group that there had been a sudden 
increase in radar echoes in the vicinity of Concord, New Hampshire shortly 
after the seeding runs. Fortunately Bemis had learned of the proposed op- 
erations and had made it a point to obtain complete radar coverage of the 

Hurricanes and Forest Fires “65s 

area in which the two planes operated. He subsequently supplied the Op- 
erations Group with a reel of 35-mm film of the radar scopes as recorded 
by his group on October 29. 

The results obtained by the radar group under Bemis emphasized 
to the members of Project Cirrus the effectiveness of this type of instru- 
mentation as an adjunct to their cloud-modification studies. It raised the 
hope that a close relationship between the two research groups might be 

In the opinion of Langmuir the result was inconclusive, because 
scattered showers began to form that day, starting in about one or two 
hours before Project Cirrus seeded. 


It was only natural that the activities of Project Cirrus should stim- 
ulate others to undertake experiments in cloud seeding. Naturally, consid- 
erable publicity resulted from Schaefer’s historic snow-making flight over 
Pittsfield in November, 1946. The fact that the Research Laboratory of the 
General Electric Company was involved took the affair out of the class of 
cheap sensationalism and provided a background of authenticity that pro- 
voked the interest of scientists and weather students the world over, as 
well as others with varying motives of interest. Continuing publicity of 
further General Electric and Project Cirrus weather research and exper- 
iment caused further interest. Many inquiries were received asking for 
information in general, and assistance in particular, in connection with 
specific projects. No attempt will be made to list all of these, but some 
are of particular interest. 


On March 24, 1947, a request for dry-ice seeding techniques was 
received from the Pineapple Institute of Honolulu, Hawaii. Although the 
records do not show it, presumably the information was needed because 
of the importance of rain on pineapple growing in Hawaii, and the Insti- 
tute wanted to keep abreast of any developments. 

At any rate, available information was supplied by Project Cirrus. 
Later newspaper accounts were received at Schenectady describing ex- 
periments carried out over the island of Molokai in 1947 by Dr. Luna 
B. Leopold and Mr. Maurice Halstead. Still later, copies of a prelim- 
inary report ) were received from these men, describing interesting 
results obtained by dumping dry ice into cumulus clouds having a tem- 
perature above the freezing point. 

Particular interest attaches to this activity, because the result of 
Leopold and Halstead prompted Dr. Langmuir to restudy some theoretical 
calculations he had prepared in 1944 at Mt. Washington. As a conse- 
quence, he developed his famous theory of the chain reaction of a rain- 
storm described‘on a precéeding page (page 43). 


For two or three seasons somewhere about 1947 or 1948 inter- 
esting experiments were conducted in the cloud seeding of thunderstorms 
with dry ice by the firm of Milliken & Farwell, a sugar company of Mo- 
bile, Alabama. Activities concentrated on big cumulus clouds in the 
neighborhood of the Mississippi delta. 

Co-operation with -68- 

Other Projects 

Information was requested from Project Cirrus, and Langmuir co- 
operated actively. He later reported very interesting results. He says 
the photographs taken are the best he had ever seen. 


On preceding pages (starting on page 39) an account is given of the 
work done by Joe Silverthorne in seeding clouds for the United Fruit Com- 
pany in Honduras. This work was carried on for the purpose of testing 
out the possibility of controlling rainfall, and particularly in the hope of 
stopping blow-downs that result from winds associated with thunderstorms, 
which occasionally destroy large stands of fruit trees. 

Langmuir visited Honduras in 1948 and 1949 and co-operated actively 
with Silverthorne. His observations convinced him of the effectiveness of 
Single pellets of dry ice in modifying large cumulus clouds; almost always 
the clouds could be profoundly modified with single pellets. (21) 


This famous case received a great deal of publicity. In order to keep 
the record straight as to what happened and the part played by Project Cirrus, 
a brief account of the case, as told by Langmuir, is incorporated. 

Although the work was done by and for New York City independently, 
it was another case of General Electric having some connection with the 
activity. When Langmuir presented a paper on weather modification to 
the American Meteorological Society in New York in 1950, New York was 
in the midst of a water shortage. Ata news conference associated with 
the AMS meeting,newsmme asked Langmuir if seeding could be of any use 
in alleviating New York’s water shortage. He replied that he knew noth- 
ing about New York; his only experience had been in the West. 

The newsmen then asked what Langmuir would advise for New York. 
He replied that the best thing for New York to do would be to get a good 
meteorologist and have him look into it. That advice was reported by the 
New York Herald Tribune. Later, when the supply of water was becoming 
less and less, this paper ran an editorial saying that things were getting 
desperate and that it was up to the city to do something about it. Seeding 
was mentioned in the editorial, and also Langmuir’s advice to get a good 

As a result, Stephen Carney, then New York’s water commissioner, 
got in touch with Langmuir and arranged for a meeting. Carney and two 
others visited Schenectady. Schaefer recommended Wallace E. Howell, 

Co-operation with -69- 
Other Projects 

director of the Mt. Washington Observatory, who had been actively associ- 
ated with Project Cirrus and the General Electric scientists even before 
the project started. Howell’s services were retained as a result. 

Howell’s experiments have never been published, and opinions vary 
about the results obtained. An interesting result was a group of lawsuits 
totaling in the neighborhood of $2,000,000. The possibility of such suits 
had been mentioned in the general discussions which preceded the actual 
seeding, and at that time Langmuir had commented that it would be entirely 
possible that such suits would be cheap compared with the results which 
might be obtained. The city, he said, had already been committed to spend 
$600,000,000 to add from 20 to 30% more water to its available supply, 
and if they could get as little as 20% more water by seeding, it would be 
worth the $600,000,000 and any interest on it. 


A tremendous amount of interest in the possibilities of controlling 
precipitation was aroused in the West, especially in the great agricultural 
regions where an adequate supply of water is highly important anda 
drought can have catastrophic consequences. Many co-operative groups 
of water users were formed, and organizations sprang up for the purpose 
of engaging in cloud seeding on a commercial basis. At the time of writing 
(May, 1952), some 350 million acres of the United States west of the Miss- 
issippi were subject to cloud seeding by commercial operators, according 
to current estimates (News release, James Stokley, for release May 12, 1952). 

Although many private individuals have undertaken to do their own 
seeding, most of this work has been done by a small number of commercial 
organizations. Topping the list is the Water Resources Development Corp- 
oration, with offices in Denver, Colorado, and Pasadena, California, whose 
rainmaking contracts were reported to cover an area of over 300 million 
acres, or about 12 times the area under irrigation in the United States. 
‘‘Farmers and ranchers paid millions of dollars for the services of this 
organization, which contemplates extending its operations to Central Amer- 
ica, South America, South Africa and Europe.’’** Others include the Pre- 
cipitation Control Company, Phoenix, Arizona; North American Weather 
Consultants, Pasadena, California; Olson & Taylor Corporation, Shelby, 
Montana; and Wallace E. Howell Associates, Cambridge, Massachusetts. 

*Page 2, Senate report #1514 (5/12/52) on ‘‘Creating an Advisory Com- 
mittee to Study and Evaluate Experiments in Weather Modification.’’ 

Co-operation with -70- 
Other Projects 

So many and so active are the organizations for this purpose, that 
there has been some concern over the effects of introducing such quantities 
of silver iodide into the atomosphere. Studies by the Research Group of 
the project indicated that silver iodide can continue in the atmosphere for 
an almost indefinite period, and although its usefulness can be modified by 
sunlight, the practical effects of such modification are not significant when 
the silver iodide is within or below the clouds. Finally, the analyses and 
calculations of Langmuir (page 55 et seq.), indicate that periodic silver- 
iodide seeding in New Mexico produced a tendency toward periodic rainfall 
and temperature fluctuations that extended significantly all over the United 

A Currently, some members of the Research Group feel that there is a 
definite possibility that some abnormal flood conditions of recent years have 
been caused, at least to a contributing degree, by commercial seeding oper- 
ations in the West. 

In addition to the commercial operators, who seed for the benefit of 
others, at least one electric power company has done extensive work in this 
field. This is the California Electric Power Company of Riverside, Cali- 
fornia. This company’s use of seeding stems from its concern over an 
adequate supply of water to operate its hydroelectric: generating stations. 
Not only does it credit the seeding with increasing its hydroelectric out- 
put by many millions of kilowatt-hours, but it also declares it has produced 
thousands of extra acre-feet of water for the city of Los Angeles. 

Interesting cloud-seeding experiments were also conducted by John 
A, Battle, consulting meteorologist of Beaumont, California, in California, 
for the San Diego County Weather Corporation and the Santa Ana River 
Weather Corporation. The experiments were conducted over the entire 
‘area of San Diego County plus the Santa Ana River drainage area in Orange, 
Riverside and San Bernardino Counties. The two corporations responsible 
represented various water agencies in those regions, where the relative 
scarcity of water makes any possibility of increasing the annual rainfall 

Silver iodide was used in the seeding. Unseeded areas were used for 
control zones, in comparison with seeded areas. About 20 per cent more 
rain fell in the target area than in the control area; in other words, 1,400,000 
acre-feet of additional water. Statistical analyses indicated that the chances 
that the cloud seeding did not have a positive effect on the precipitation meas- 
ured varied anywhere from 12-to-1 to 10,000-to-1, depending on the area 

Co-operation with -71- 

Other Projects 


Active research in cloud seeding has been carried on in many for- 
eign countries. Again, the work was stimulated by the reports of success- 
ful tests made by Project Cirrus, and in virtually all cases the foreign 
work was based on information either obtained by direct contact with 
Project Cirrus or through the study of published data. 

Among the foreign countries engaged in such work are Canada, 
Cuba, Peru, England, France, Switzerland, Israel, Algeria, Tanganyika, 
Union of South Africa, Formosa, Japan, and Australia. (Schaefer has 
reports covering some of these operations.) 


Contract DA36-039-sc-15345 (the last of a series) terminates Sept- 
ember 30, 1952, after a little over five years of the active life of Project 
Cirrus as a government-sponsored activity. By that time all the early 
exploratory phases of cloud seeding and allied research concerned with 
the physics of clouds were virtually complete. So many other research 
projects had been stimulated that continued progress in the search for 
new basic knowledge of weather phenomena Seems assured. 


It is not, of course, easy to predict the ultimate results of the 
work done by Project Cirrus. But it seems certain that the pioneering 
and spectacular work of the General Electric scientists in cloud physics, 
cloud seeding and weather modification will eventually have a profound 
influence on domestic and world economics. 

Says the report accompanying S.2225 (footnote page 69): 

“Tf practical, weather control promises tremendous 
benefits for a small investment. Research work in the 
field involves no test plants or production facilities and 
very little expensive equipment. The seeding agents, car- 
bon dioxide or silver iodide, are inexpensive, yet when used 
in small quantities they apparently produce weather phenomena 
of the highest magnitude. If these phenomena cause only a 
Small increase in precipitation, this small increase can be 
economically important. 

*fAn inch of rain, converted into runoff and concentrated 
into a reservoir, can produce electric power worth hundreds 
of thousands of dollars. A small fraction of an inch of extra 
rain, falling on crops during the period of germination, can 
greatly increase crop yields. But artificial nucleation may 
have useful potentialities in addition to that of stimulating 
rainfall. It may have possibilities for increasing snowpack 
in mountainous areas, for holding back and ‘softening’ rain- 
storms, thereby reducing soil erosion, for inhibiting hail, for 
breaking up hurricanes, and for precipitating out and thereby 
cutting holes in clouds so that aircraft can operate.’’ 

Some of the possibilities inherent in cloud seeding as evaluated 
by Project Cirrus scientists follow: 

Widespread Weather Modification. The results of the various New 
Mexico tests, coupled with observations of the effects of other ground 
seeding with silver iodide, point to significant possibilities in the 

Conclusion -74- 

widespread modifying of weather conditions. Such work could easily have 
profound economic, political, and military effect. 

Modifying Orographic Clouds. Orographic clouds, which form as 
moist air is forced to rise when it encounters a barrier such as a mountain 
range, are very common in mountainous regions, and they often form contin- 
uously for many days. Relatively little precipitation from them reaches the 
earth, except as rime deposits on trees and rocks or as scattered snow 
crystals. If techniques could be devised to cause a widespread and effective 
precipitation of such clouds, the depth of the snow pack in the vicinity of 
mountains might be markedly increased. Such a result would be of much 
importance, since the snow pack on mountain slopes is very valuable in 
stabilizing the streams which flow from such regions. These streams, in 
turn, have great Significance from a standpoint of electric power and water 
supply. The work done by the California Electric Power Company (page 70) 
is an important contribution to this knowledge. 

Producing Regions of Ice Nuclei. The production of specific regions in 
the free atmosphere containing high concentrations of ice nuclei or potential 
ice nuclei is an interesting possibility. Cold middle clouds, even though having 
no appreciable moisture, may be used as ‘‘holding reservoirs’’ to store ice 
crystals until they come into contact with lower clouds of greater thickness 
or are entrained into cool or cold cumulus. 

An example of this type of seeding occurred during the hurricane seeding 
project in October, 1947 (page 61). A relatively thin layer of stratus clouds 
covering an area of nearly 300 square miles was transformed to snow crystals. 
The subsequent fate of the crystals is still a moot question, but if a considerable 
region of them was entrained into the lower levels of a line of towering cumulus 
observed during the flight and situated in the southeast quandrant of the storm, 
the entrainment might have exercised a profound effect on the subsequent 
development of those cumulus clouds. 

Similarly, the ice crystal residue from seeded, but small, cumulus clouds 
may be entrained at a low level into much larger cumulus ferming in their vici- 
nity. In this way, an effect of considerable magnitude is produced as the super- 
cooled regions are infected at a lower level than would otherwise be possible. 

It will take much careful study to establish methods for utilizing this 
type of seeding. Eventually, it may become of great importance, 

Modifying Stratiform Clouds. The widespread modification of stratus 
clouds by artificial means is possible at the present time whenever such clouds 
are Supercooled. Under such conditions, the clouds may be either further 
stabilized by overseeding, or precipitation may be triggered by using the op- 
timum number of ice nuclei. 

Conclusion =O= 

Observed results of the seeding of stratus clouds indicate that holes 
can be cleared in them by this method, which is bound to be of value in 
aircraft operations. 

Modifying Supercooled Ground Fogs. Supercooled ground fogs formed 
by advection or radiation may be modified and even dispersed if care is 
exercised to prevent overseeding. Too high a concentration of ice nuclei 
introduced into such fogs might actually make the fogs worse. 

The prevention of the formation of ice fog is another possibility 
from the proper manipulation of seeding techniques. By introducing an 
optimum number of sublimation nuclei into the air in regions where such 
fogs are troublesome, it may be possible to continuously remove from the 
air the moisture responsible for the formation of this interesting but of- 
ten troublesome type of ground fog. 

The ice crystals generated in the vortices of airplane propellers 
plus the moisture added to the air by the combustion exhaust of the plane 
are the causes which generally lead to the formation of ice fogs at air- 
ports. Whether the removal of supersaturation with respect to ice by 
seeding methods will be of sufficient magnitude to prevent the ice-fogging 
effects produced by plane operations can be determined most conclusively 
by actual experiment. 

Protection of Aircraft. There is no question about being able to 
modify icing clouds in the vicinities of airports and along heavily traveled 
air lanes. The problem rather, is whether it may have a practical appli- 
cation. Low clouds which restrict visibility for landing approaches around 
airports, thick clouds in which planes must cruise as they wait for per- 
mission to land, and thick clouds which might deposit a serious icing load 
on the plane as it tries to climb up through them--these comprise hazards 
to safe plane operations. And when such clouds are supercooled, they may 
be profoundly modified. 

The simplest means for carrying out such cloud modification would 
be to employ a plane well equipped for flying under serious icing condi- 
tions for patrolling the air lanes. The plane would report weather and 
cloud conditions and, whenever serious supercooled clouds occurred, 
would carry out seeding operations. 

In flying through a supercooled cloud, the airplane itself may pro- 
duce a fairly effective modification. The vortices which form at the 
trailing edges of the wings and particularly from the propeller tips form 
large numbers of ice crystals. 

Conclusion -(6= 

Modifying Orographic Thunderstorms. It may be possible that silver- 

iodide seeding from ground generators would be particularly useful in mod- 
ifying orographic ‘‘towering’’ cumulus to prevent their growth into thunder- 
storms. By determining the air trajectory from the ground into the cold 
part of the cloud, potential ice nuclei may be sent aloft by a very simple 
procedure. If subsequent experiments indicate that it is important to seed 
such clouds at a temperature only a few degrees colder than the freezing 
point, it may become necessary to use dry ice dispensed from planes or 
carried into the clouds by free balloons or projectiles. 

Modifying Towering Cumulus. Towering cumulus also forms over 
flat country at times when the atmosphere is conditionally unstable. Dan- 
gerous and often deadly lightning strokes, torrential rains, destructive 
winds, and sometimes hail and tornadoes are the end products of such 
developments. Since the high, vertical thickness of a supercooled cloud 
seems to be the basic requisite in the formation of a thunderstorm, it may 
be quite feasible by proper seeding methods to prevent this phase from 

The manner in which the seeding is done may produce a wide vari- 
ation in the end results obtained. By seeding each cumulus tower with 
large numbers of crystals shortly after it rises above the freezing level, 
the cloud would be continuously dissipated and no extensive regions of 
supercooled cloud could develop. On the other hand, it might be desirable 
to seed such clouds to realize the maximum possible energy release. This 
presumably would involve seeding each cumulus tower just previous to 
the point of its maximum development. If this could be done effectively, 
it might be possible to build the storm into a much larger one than would 
develop under natural conditions. 

Preventing Hail. The possibility that hailstorms might be prevented 
by seeding techniques is of considerable economic importance. A great 
amount of basic information is needed on the various properties of storms 
that produce hail. In some parts of the country where severe hail damage 
is frequent, storms are formed over certain mountain ridges and peaks 
that serve as cloud breakers. Such clouds should be particularly suited 
for modification by ground generators, since the air trajectory is definitely 
related to the flow of air up the mountain and into the clouds. 


As in any of the physical phenomena, there are definite limitations 
to the degree in which experimental meteorology may be employed in mod- 
ifying clouds in the free atmosphere. Some of these apparent limitations 
may disappear as our knowledge increases, although most of the restrictions 
now recognized are imposed by known physical laws. 

Conclusion -77- 

Fair Weather Cumulus. Foremost of these restrictions is the factor 
of cloud type and size. Certain clouds, such as the fair-weather cumulus, 
have such a small volume and restricted area that, even though they are 
easily modified when supercooled, their total liquid-water content is incon- 
sequential. Another complicating factor is that the air below larger clouds 
is sometimes So dry that a considerable amount of precipitation evaporates 
before it reaches the ground. 

Warm Ground Fog. Another type of cloud which is difficult to modify 
is the warm ground fog formed by radiation or advection. Such fogs are 
often extensive and of considerable economic importance, especially from 
the standpoint of airplane traffic control. But the natural structure ofa 
fog precludes any simple method of modifying it. Generally, the vertical 
thickness is not more than 100 meters or so, with a cloudless sky above. . 
This rules out the possibility of modifying from above by forming precip- 
itation in higher clouds to ‘‘rain out’’ the fog. (But supercooled ground 
fogs may be modified, as explained on page 75.) 

Drought. Another weather situation where no method of relief is 
now apparent is in the case of drought. This condition generally results 
from the stability of a complex weather pattern in a manner which, at 
present, is not very well understood. Drought is generally accompanied 
by either cloudless skies or clouds of small vertical and horizontal devel- 
opment, because of strong inversions or thick layers of dry air. 

Convergence. The development of convergence is an important 
feature in the formation of appreciable amount of rainfall in many parts 
of the world. As a rule, such developments are generally accompanied 
by the occurrence of natural precipitation, which continues So long as 
the convergent movement is present. About the only thing that artificial 
modification of clouds might do under such atmospheric conditions is 
to initiate the precipitation cycle a few hours before it would start nat- 
urally, or under some conditions, to delay the onset of precipitation by 


As is so often the case with the proposal of striking or revolu- 
tionary new concepts in science, the validity of the observations and 
conclusions of the members of the Research Group, both before and 
after the establishment of Project Cirrus, was challenged by many. 
As a result, quite a school of opposing thought has been built up. This 
is a normal, healthy condition of affairs in a free economy, and the 
results would be of no particular consequence were it not for the fact 
that the possibilities inherent in artificial weather modification have 
such great economic and military significance. 

Conclusion -78- 

Although criticism and challenge have by no means been confined to 
any one person or group, the spearhead of the opposition, so to speak, has 
been the United States Weather Bureau. This unit has kept a watchful eye 
on all the developments associated with Project Cirrus. In many cases 
it designated observers to work with the project on specific operations. 

It has conducted experiments of its own, to test the validity of Project 
Cirrus findings, notably the Cloud Physics Project, jointly conducted by 
the Weather Bureau and the United States Air Force. 

The running controversy between representatives of the Weather 
Bureau and Dr. Langmuir is summarized in an article(26) available in 
his office files at The Knolls. In it Langmuir discusses and answers the 
various criticisms and challenges. He summarizes the importance of 
the situation in the following paragraphs. 

‘‘The possibility of such wide-scale control of weather 
conditions, of course, offers important military applications, 
but since nearly all meteorologists are much influenced by 
the opinions and the attitudes of the Weather Bureau men, 
the opposition on the part of the Weather Bureau and other 
groups has, up to the present, prevented the starting of any 
military applications. 

‘Tt was, therefore, of the utmost importance to clear 
this matter up without getting too much publicity. It is 
largely for this reason that no detailed accounts of the evi- 
dence in favor of the reality of the wide-scale effects have 
been published....’’ 

Langmuir has since explained orally that, in view of this situation, 
he has resorted to the use of publicity only when other methods of bringing 
matters to a head had failed. At the time of the preparation of this report, 
however, both he and the other scientists associated with Project Cirrus 
had begun to feel that the opposition was beginning to ‘‘see the light’? and 
that it would only be a matter of time before the Weather Bureau would 
change its attitude. It is believed that the results obtained by the Cali- 
fornia Electric Power Company (page 70) have had a great deal to do with 
that change of attitude. 

Some picture of the Weather Bureau side of the controversy may be 
found in testimony 93 presented during hearings before Senate subcommittees 
on three bills, as follows: 

S.5, a bill to provide for research into and demonstration 
of practical means for the economical production, from sea or 
other saline waters, or from the atmosphere (including cloud 
formations), of water suitable for agricultural, industrial, 

Conclusion BO i= 

municipal, and other beneficial consumptive uses, and 
for other purposes. 

8.222, a bill to provide for the development and reg- 
ulation of methods of weather modification and control. 

S. 798, a bill to authorize the Secretary of Agriculture 
to conduct research and experiments with respect to methods 
of controlling and producing precipitation in moisture- 
deficient areas. 

The attitude of the Weather Bureau is summarized in a statement 
presented to the above groups on March 14, 1951, by W. F. McDonald, 
assistant chief of the United States Weather Bureau, and a further clari- 
fication of Weather Bureau views is found in the subsequent questioning 
of Mr. McDonald by members of the committees. 

The fact that the challenges to the validity of Project Cirrus claims 
are not confined to the Weather Bureau is also indicated during the same 
Senate hearings. Statements were made at those hearings by other indi- 
viduals not associated with the Weather Bureau, and some of those individ- 
uals did not agree with the findings of Project Cirrus. Among them were 
Hans H. Neuberger, professor of meteorology and chief of the Division 
of Meteorology, Pennsylvania State College, and Charles L. Hosler, a 
staff member of that college; and Henry G. Houghton, professor of meteor- 
ology and head of the Department of Meteorology, Massachusetts Institute 
of Technology. 


For various reasons, national legislation has been suggested, and 
actually introduced, to regulate and control artificial weather modification. 
Of the three bills referred to in the preceding paragraphs, two (S.222 and 
S.798) specifically covered this proposed regulation and control (S.222) 
and authorized the Secretary of Agriculture to conduct research and ex- 
periments (S.798). 

Since that time a new bill was drafted and introduced in the Senate, 
82d Congress, second session: 8.2225. This bill would create a tempor- 
ary advisory committee of nine persons to study and evaluate experiments 
in weather modification, continuing no longer than July 30, 1955. The com- 
mittee would report to Congress at the earliest possible moment on the 
advisability of the Government regulating, by means of licenses or other- 
wise, the activities of persons attempting to modify the weather. The ad- 
visory committee would consist of five members appointed from public 

Conclusion -~80= 

life by the President plus the secretaries of Defense, Interior, Agriculture, 
and Commerce, or their designees, The bill was referred to the Committee 
on Interstate & Foreign Commerce on October 8, 1951, and reported out 
with amendments on May 12, 1952. 

The General Electric attitude toward legislation was summed up at 
the above hearings by Vice President and Director of Research, C. G. Suits, 
and by Schaefer and Vonnegut, who accompanied him to the hearings. Said 
Suits, in part: 

‘“These facts which underlie experimental meteorology 
are not in the controversial area; they have been demonstrated 
and proven. What controversy has arisen has been concerned 
with such matters as (1) the economic importance of induced 
rainfall--by ‘induced rainfall’ I mean artificially induced rain- 
fall--(2) whether long-range effects of cloud seeding exist, 
and (3) whether induced rainfall may not have occurred nat- 
urally in the absence of seeding. There is a great mass of 
information bearing on these questions, and it would not be 
possible to discuss it all here. 

‘Tt is my considered opinion, however, that the results of 
the most recent work are of the very greatest importance to the 
Nation. We have at hand a means of exerting a very considerable 
degree of control of weather phenomena. Precisely how much 
control can be accomplished will come from further study. Much 
work remains to be done, and it would be a national tragedy if 
legislation did not provide a proper frame work for developing 
the full potentialities of weather modification methods. It would 
be hard to imagine anything more important to the country than 
weather modification and control.’’ 

Another extract from the Suits statement: 

‘I wish to be very clear on one point. The work my com- 
pany has done in this field, initially at our own expense and more 
recently under a Signal Corps contract with the participation 
of the Office of Naval Research and the United States Air Force, 
has had no single practical application within the Company. The 
work originated as an unexpected result of one of the many fun- 
damental investigations which we undertake in the search for 

. new knowledge. It was continued because the leaders of my com- 
pany and responsible representative of the Government believed 
that the possibilities of weather modification might be of great 
importance to the Nation as a whole. On December 27, 1950 my 

Conclusion =Sil= 

‘company announced that for the present and until further 
notice it does not intend to enforce any of its patents re- 
lating to weather modification by the artificial production 
of snow and rain. 

‘‘A contractor of the Government for research in this 
field, where the general public is the Intended beneficiary, 
should not be subjected to the uncertainties of legal liability 
hazards which are inherent in experimental weather modifi- 
cation. The provisions of 8.222 would greatly minimize the 
legal hazards which now exist. Some such solution of this 
problem must be found if private agencies are to engage in 
research in this field, and by that I mean under contract 
with the Government.’’ 

Other aspects of the need for legislation were voiced at that time 
by Schaefer. The following quotes from his statement illustrate these 
other aspects: 

“Tt is very important, in my opinion, that weather 
studies involving experimental meteorology be conducted 
in such a manner that all of the modifications attempted 
by man-conducted seeding operations be known and con- 
trolled. If this is not done, the effort of attempting to - 
understand the reactions which occur is a hopeless one... 

‘It is obvious that some type of national legislation 
is of the utmost importance at this time to protect the 
public in the future from unscrupulous individuals who 
would play on the gullibility, hope, or desperation of in- 
dividuals or groups in need of water or other relief from 
an undesirable climatic situation.”’ 

Vonnegut, also, in his statement read at those hearings, urged 
the adoption of suitable legislation. In addition to the reasons voiced 
by Suits and Schaefer, he added others, which are found in the follow- 
ing extract: 

*“The problems of weather control are so large and 
of such Nationwide importance that only Federal legisla- 
tion can insure that this powerful new tool will result in 
the greatest good for the largest number of people. In the 
absence of this legislation, I believe that the development 
of the benefits to be derived from cloud seeding may be 

Conclusion -62- 

‘greatly retarded or prevented and that possibly much harm 
can result from storms, droughts, or floods produced by un- 
controlled seeding. | 

‘‘Theory has predicted and experiments are confirming 
the fact that a few pounds of silver iodide released into the 
atmosphere in the form of fine particles can exercise a pro- 
found influence over the weather hundreds d miles away from 
the point of release. Clearly no private individual or group 
can be permitted to carry on operations likely to affect weather 
conditions over thousands or hundreds d thousands of square 

‘*The potentialities, both for good and bad, which attend 
silver-iodide seeding are so large that the development and 
use of this technique must be placed in the hands of the Fed- 
eral Government. 

‘Secondly, it is highly desirable that the Government 
pass laws regulating cloud seeding, in order to promote the 
rapid development of this science. Many facts are yet to be 
learned concerning the best methods of seeding to obtain 
desirable results. These facts can be determined only by 
experiments in the atmosphere. The analysis of the results 
of cloud-seeding experiments is a complicated and difficult 
problem. If, as in the case at present, many Seeding ex- 
periments are being independently and simultaneously carried 
out in many places, the problem of analysis becomes even more 
difficult and frequently impossible. Federal regulation is nec- 
essary to insure the rapid development of the benefits: of 
cloud seeding. 

‘‘Thirdly, the science of weather control can be of such 
great benefit to the entire country that the responsibility 
for its advancement must rest with the Government. Legis- 
lation should provide funds for research by Government and 
by private groups into fundamental scientific problems con- 
nected with the weather.”’ 

At the time of the preparation of this history, no national legislation 
had yet been enacted to cover any of the needs outlined in the foregoing. 

Conclusions -83- 


A wealth of information, published and otherwise, is available to pro- 
vide further details of the various aspects of this project as covered in 
this history, and most of it is listed in AppendixIV. Some of this information 
accompanies this report in the form of various appendices--either because 
the information is so closely associated with history that it should become, 
at least to that extent, a part of it, or because it would be difficult to refer 
to otherwise. 

A summary of other types of supplemental information follows: 

1. Government Reports. The various quarterly, final, and occasional 
reports made by the General Electric Company to the Government summarize 
the work conducted under various Government contracts. These reports have 
all been printed and are available in General Electric libraries and files. 

2. Articles & Papers. Many articles and papers have been prepared 
by members of Project Cirrus, especially members of the Research Group, 
for printing in periodic publications or for delivery before scientific and 
other bodies. Some of these, covering significant developments or making 
helpful summaries of progress but not specifically included in the reports 
to the government, are listed in Appendix IV. 

3. Laboratory Records. A further wealth of detailed information is 
to be found in the normal records of the Research Laboratory. In partic- 
ular, the notebooks maintained by the individual workers in the project can 
be consulted. In addition to these are the reports of the Steering Committee 
and the Operations Group of Project Cirrus, copies of some or all of which 
are in the possession of Langmuir, Schaefer, and Maynard. Still other infor- 
mation can be obtained from letterbooks, contract folders, and accounting 

4, Langmuir’s Records. A great deal of pertinent information has 
been gathered together by Langmuir as the basis of his various analyses 
and mathematical calculations, particularly in connection with his running 
controversy with the Weather Bureau. One such collection 26) has already 
been mentioned. Another17) is a collection of unpublished letters and 
reports on the general subject of the seven-day periodicity in the weather 
during 1950. Both of these documents are to be found in Langmuir’s office 
files at The Knolls. 


Appendix | 

Alphabetical List of Personnel 

Mrs. Margaret Bakuzonis, GE 

Raymond Bellucci, civilian mathematician 

S/Sgt. C. S. Belote, USAF, radio operator 

S/Set. Roy E. Berry, USAF, crew chief 

George Blair, GE 

Duncan Blanchard, GE 

Major D. Blue, USMA 

1st Lt. Mitchell B. Bressette, USAF, navigator 
Vincent Bruck, Signal Corps photographer 
Robert C. Bulock, Signal Corps 

Major E. Cartwright, USAF 

Theodore Catellie, Signal Corps photographer 
Capt. Clarence N. Chamberlain, Jr., USAF, pilot 
T/Sgt. Vernon H. Davis, Signal Corps Supply Sgt. 
M/Set. Eugene R. Dickson, USAF, crew chief 
Mrs. Analee Durant, secretary 

Robert F. Egger, AL2, USN, radio and radar operator 
Raymond Falconer, GE 

Lt. Cdr. Elwood B. Faust, USN pilot 

Charles S. Ferris, civilian electrician 

Victor Fraenckel, GE 

S/Sgt. Russell C. Friedl, USAF crew chief 

lisp int, Carl Jd. Pubrmann, USA pilot 

Myer Geller, GE 

Miss Constance Godell, secretary 

m/5 Cue, Hallissienal Corps driver. 

Cpl. Francis N. Ham, Signal Corps driver 

ii Cdr, Bake Harrison, UsNitpilor 

list Lt, Ted E. Hoffman, USAFE pilot 

T/Set. C. E. Hughey, USAF crew chief 

Thomas J. Hurley, Signal Corps photographer 
Lt. J. W. ller, USN pilot 

Cpl. Billy G. Jackson, Signal Corps photographer 
Cpl. Ernst S. Johnson, Signal Corps photographer 
T/Sgt. Martin M. Kalich, USAF radio operator 
John Kelly, Signal Corps civilian technician 
Major Rudolph C. Koerner, Jr., Signal Corps 
Cpl James W. Land, Signal Corps Supply Set. 
Dr. Irving Langmuir, GE 

William Lewis, U.S. Weather Bureau cons. 

Appendix I 


Kiah Maynard, GE 

AERM1 E. R. Millan, USN aerologist 

S/Sgt. H. E. Millett, USAF crew chief 
Landon Morris, Signal Corps photographer 
Raymond L. Neubauer, GE 

S/Sgt. J. H. Niven, USAF radio operator 
William N. Perry, ADC, USN pilot 

Capt. John A. Plummer, USAF pilot 

Harold Pontecorvo, Signal Corps photographer 
Alexander Preede, Signal Corps photographer 
T/Sgt. William M, Ratcliffe, USAF crew chief 
Carl R. Remscheid, AG1, USN aerologist 
Lt. Cdr. Daniel F. Rex, USN 

Edward Rudzik, AD3, USN engineer 

AERMI1 R. F. Rayan, USN aerologist 

Capt. Michael A. Sbarra, USAF pilot 

Dr. Vincent Schaefer, GE 

Lt. Cdr. Paul J. Siegel, USN pilot 

Robert Smith-Johannsen, GE 

Donald Southard, Signal Corps photographer 
Samuel Stine, Signal Corps 

George Swistak, Signal Corps photographer 
ACMM Adam Szepkowsky, USN chief 

Lt. Gdr, C, EB. Tilden, UsN 

Lt. David D. Tracy, USAF navigator 

Ist Lt. Henry W. Tutt, USAF pilot 

Dr, Bernard Vonnegut, GE 

Howard J. Wells, AGC, USN aerologist 
CAERM G. B. West, USN, aerologist 

Roger Wight, Signal Corps (civilian) 

Capt. Carl F. Wood, USAF pilot 

Charles Woodman, GE 


Project Cirrus Unnumbered Flight Tests 

Date Location Operation 

11/13/46 Pittsfield DI seeding 

Taye) Schenectady DI seeding, isolated cumulus 
11/29 Schenectady DI seeding, isolated cumulus 
12/20 Schenectady DI seeding 

3/6/47 Schenectady DE seeding 

S/T Schenectady DE séeding 

Bye Schenectady DE seeding 

4/7 Schenectady DE seeding 

5/8 Schenectady DI and SI seeding 

8/5 Schenectady Instrument Check 

8/6 Schenectady Instrument Check 

8/7 Schdy-Westover, Mass. Weighing 

8/11 Schenectady Instrument calibration 
8/13 West Point DI and SI seeding 

8/15 Schenectady SI seeding 

8/18 Schenectady Instrument check 

8/20 Schenectady Instrument check 

8/21 Schdy-Indian Lake DI and SI seeding 

8/25 Schenectady DI and SI seeding 

8/27 Schenectady Instrument check 

8/28 Schenectady Instrument check 

8/29 Schenectady Instrument check 

9/19 Schenectady Dry run for hurricane 
9/25 Schenectady Instrument check 

9/30 Schenectady Instrument check 

OAT Schenectady Tracing SI 

10/10 Schdy-Mitchell Field Hurricane study 

10/11 Olmstead, Pa.-Brookley, Ala. Hurricane study 

O12 Brookley-McDill, Fla. Hurricane study 

10/13 Florida Hurricane study 

10/14 MeDill-Olmstead, Pa. Hurricane study 

OVALS Olmstead-Schdy Hurricane study 

5/31/48 Schenectady Water drop tests, pumping 
6/2 Schenectady Water drop tests, balloons 
10/18 Schenectady DI seeding 

1/30 Schenectady Stereoscopic camera test 
12/14 Schenectady Info. Flight #3 - balloon soundings 

Observation - tie-in with 
Ground Operation #75 

2/7/50 Boston-Schenectady 

Appendix II 
Numbered Test Flights 


Number Date 





New Hampshire 
Olmstead,Pa; Brookley,Ala. 


Middletown, Pa. 



Sacanadaga Reservoir 

Cape Cod 


Off New Jersey Coast 

Lake George 
Glens Falls 

Catskill N.Y. 



DI seeding 

Forest-fire seeding; Oper. Red 

Water seeding 
Racing SI 

SI seeding 

DI seeding 

DI pattern seeding 
DI seeding 



DI pattern seeding 
DI pattern seeding 

DI seeding 

DI pattern seeding 
DI seeding 

DI pattern seeding 
DI seeding 

DI seeding 

DI seeding 

DI pattern seeding 

DI seeding--MIT project 


Water seeding 

DI pattern seeding 
DI seeding 

DI cumulus seeding 
Water seeding 

DI seeding 

DI and water seeding 
DI seeding 
DI and water seeding 

DI seeding 

Water seeding 
Water seeding 
DI and water seeding 
DI seeding 
DI and water seeding 
Water seeding 

Appendix II 









Lake George 
Albuquerque, N.M. 
Albuquerque, N.M. 

Fast of Albany 

Schdy and Amsterdam, N.Y. 

Schdy and Rome, N.Y. 
Schdy-NW of Albany 
S of Utica 

N of Schenectady 

E of Albany 

Albany & East 

W of Coxsackie 
Puerto Rico 

Puerto Rico 

Puerto Rico 

Puerto Rico 

Puerto Rico 

Puerto Rico 

Puerto Rico 

Puerto Rico 

Puerto Rico 

Puerto Rico 

Puerto Rico 

S of Lake Ontario 
Sprakers, N.Y. 

W of Syracuse 

Ines IDibs, IN GIES es seSiablrcial 

Schdy -Rome-Middletown- 

E of Albany 
Albany vicinity 



Water ice and DI seeding 
SI and DI seeding 
Water ice and DI seeding 
Water ice seeding 

DI seeding --pattern 

DI seeding --pattern 

DI seeding --pattern 

DI pattern seeding 

DI pattern seeding 

DI pattern seeding 

DI pattern seeding 

DI seeding 

DI seeding 

SI & DI seeding; pattern 
DI seeding; pattern 

DI seeding; pattern 

Survey & water seeding 
Water seeding 


Water seeding 







DI & SI seeding; pattern 
Temperature soundings 
SI seeding; pattern 

DI seeding 

Testing vortex thermometer 

Temperature soundings 

Testing cloud meter; photo. 

Testing vortex thermometer 

DI pattern seeding 
DI pattern seeding 

Testing vortex thermometer 

DI seeding 

Appendix II 






West Point & return 


Rome, N.Y. & return 

Ashokan Reservoir 

Little Falls & Rome 


Schdy-Rome & return 

Ballston Spa 
Winchester, Vt. 
Albuquerque, N.M. 
Albuquerque, N.M. 
Albuquerque, N.M. 
Albuquerque, N.M. 
Albuquerque, N.M. 
Albuquerque, N.M. 
Albuquerque, N.M. 
Albuquerque, N.M. 
Albuquerque, N.M., 
Albuquerque, N.M. 
Schoharie Valley 
Schoharie Valley 
Schoharie Valley 
Schoharie Valley 
Schoharie Valley 


E. of Schdy 


SI pattern seeding 

Testing vortex thermometer 
Instrument testing 


Testing condensation nuclei meter 
Instrument testing . 

DI seeding 

Instrument testing 

Instrument testing 

Instrument testing 

Instrument testing 

Instrument testing 

Testing condens. nuclei counter 
Instrument check 

Testing vortex thermometer | 
Testing vortex thermometer, high altituc 
Salt water seeding 
DI seeding 

Instrument test 

Instrument test 

DI seeding 

DI, liquid CO, & water seeding 

DI & liquid CO, seeding 

DI seéding 

DI & SI seeding 

DI seeding 

SI ground & DI air seeding 

SI ground & DI air seeding 

SI ground & DI air seeding 

SI ground & DI air seeding 

Observing ground seeding 

Observing ground seeding 

Observing ground seeding 

Observing ground seeding 

Observing ground seeding --tie-in 

Gd: Op, #13 

Testing vortex thermometer 

Testing vortex thermometer 

Testing vortex thermometer --tie-in 
Gd. Op. #16 

DI seeding; Gd. Op. #17 

Temperature Sounding; Gd. Op. #24-25 

Appendix II 


Number Date 
23 10/13 
124 10/18 
5) 10/17 
ILS) 10/24 
127 Tsib/AL 
128 LLL) 
129 AAG 
130 Hal alee 
Ss 1/6 
WZ, 11/30 
33 1/30 
134 LAyak 
5) PY Ne 
136 12/15 
Si 12/16 
138 1/4/50 
139 1/20 
140 1/30 
AR 1/30 
142 Oe 
143 2/6 
144 DMO 
145 2/20 
146 2/28 
147 2/28 
148 3/3 
149 8/17 
150 3/20 
ISL 3/21/50 
Iz By 22, 
ILS) 4/10 
154 4/12 
155 4/18 
156 4/19 
Ney 4/25-26 
158 5/8 
159 5/28 
160 6/6 
161 6/23 
162 6/26 




Indianapolis -Schdy 

Cape Cod 

Mt. Washington 
Schdy-Mt. Washington 
Schdy-Dayton, O. 

Schdy -Boston-Bangor- 
Massena -Rochester- 

Mt. Washington 

N of Schenectady 
E Troy & Albany 
Albuquerque, N.M. 
Albuquerque, N.M. 


Instrument testing; Gd. Op. #26 

Temperature soundings; Gd. Op. #34 

Temperature soundings; Gd. Op. #34 
Observation; FO-39 



Instrument test; GO-41 

Instrument test; GO-46 

Instrument test & Weather Observation 
Instrument test; GO47-48 
Calibrating vortex therm; GO-53-54 
Snow replicas; vortex therm; GO-55 
DI seeding; joint with MIT 

SI detection; GO-63 

Instrument check; DI seeding 

Snow replicas; GO-71 

Calibrating vortex therm.; GO-71 
DI clear-air seeding 

Snow replicas; vortex thermometer 
Photos; snow replicas 

Clear-air seeding 

DI seeding; snow replicas 

DI seeding; snow replicas 
Attempted vapor trails 

Instrument Calibration 

Snow replicas 

Weather reconnaisance 

Weather reconnaisance 

Snow replicas 

SI seeding; GO-83 


SI seeding 

SI seeding 

SI seeding 

DI clear-air seeding 
DI seeding 

DI cumulus seeding 
DI cumulus seeding 

Appendix II -92- 

Number Date Location Operation 
163 6727 Albuquerque, N.M. DI cumulus seeding 
164 6/27 Albuquerque, N.M. DI cumulus seeding 
165 6/28 Albuquerque, N.M. DI cumulus seeding 
166 6/29 Albuquerque, N.M. DI cumulus seeding 
167 6/30 Albuquerque, N.M. DI cumulus seeding 
168 Vic Albuquerque, N.M. DI cumulus seeding 
169 5 Albuquerque, N.M. Tracing gd. SI; DI seeding 
LAO 1/6 Albuquerque, N.M. Tracing gd. SI; DI seeding 
qa ol Albuquerque, N.M. DI seeding 
he 7/8 Albuquerque, N.M. DI & SI seeding 
Ts vival Albuquerque N.M.- Gathering weather data 
Burbank, Calif. 
ARS oe Ae Burbank-Gt.Falls,Ont. Gathering weather data 
aS TANS) Gt. Falls-Schdy Gathering weather data 
176 10/26 Mt. Washington DI seeding (joint) 
eT 5/15/51 Mt. Washington SI seeding (joint) 
178 4/8 Schenectady: SI & DI seeding 
179 4/24 Schenectady Observation 
180 5/9 Schenectady DI, Liquid CO,, & SI seeding 

181 Sy Alls Schenectady DI & SI seeding 

Number Date 





Ground Operations 


Schdy Co. Airport 
sichdy. Con Airport 
Sehdy Co. Airport 
Sehdy Co. Airport 
Schdy Co. Airport 

Albuquerque, N.M. 

Schoharie Valley 
Schoharie Valley 
Schdy Airport 

Schoharie Valley 
Schoharie Valley 
Schoharie Valley 
Schoharie Valley 
Schoharie Valley 
Schoharie Valley 
Schoharie Valley 
Schoharie Valley 
Schoharie Valley 
Schoharie Valley 
Schoharie Valley 
Schdy Airport 

Schoharie Valley 
Schoharie Valley 
Schoharie Valley 
Schdy Airport 

Schoharie Valley 
Schoharie Valley 
Schoharie Valley 
Sehdy Airport 

Schoharie Valley 
Schoharie Valley 
Schoharie Valley 
Schoharie Valley 
Schoharie Valley 
Schoharie Valley 
Schoharie Valley 
Schoharie Valley 
Schoharie Valley 
Schoharie Valley 
Schoharie Valley 


Cloud photography (still) 
Cloud photography (still) 
Cloud photography (still) 
Cloud photography (still) 
Lapse-time movies 

SI seeding 
SI seeding 
SI seeding 
SI seeding 
SI seeding 
SI seeding 

SI seeding--tie-in Flight #117 

SI seeding 

SI seeding 

SI seeding --Flight #120 
SI seeding--Flight #121 
SI seeding 

SI seeding 

SI seeding 

Lapse-time movies 

SI seeding 

SI seeding 

SI seeding --Flight #122 
Lapse-time movies 

SI seeding--Flight #1238 
SI seeding--Flight #124 
SI seeding 

Lapse-time movies 

SI seeding 

SI seeding 

SI seeding 

SI seeding--Flight #127 
SI seeding 

SI seeding 

SI seeding 

SI seeding 

SI seeding 

SI seeding--Flight #128 
SI seeding 

Appendix ITI 




2 fal 


Schoharie Valley 
Schoharie Valley 
Schoharie Valley 
Schoharie Valley 
Schoharie Valley 
Schoharie Valley 
Schoharie Valley 
Schdy Airport 

Schdy Airport 

Schoharie Valley 
Schoharie Valley 
Schoharie Valley 
Schoharie Valley 
Schoharie Valley 
Schoharie Valley 
Schoharie Valley 
Schoharie Valley 
Schoharie Valley 
Schoharie Valley 
Schoharie Valley 
Schoharie Valley 
Schoharie Valley 
Schoharie Valley 
Schoharie Valley 
Schoharie Valley 
Schoharie Valley 
Schoharie Valley 
Schdy Airport 

Schoharie Valley 
Schoharie Valley 
Schdy Airport 

Schoharie Valley 
Schoharie Valley 
Schoharie Valley 
Schoharie Valley 
Schoharie Valley 
Schoharie Valley 
Schoharie Valley 
Schoharie Valley 
Schoharie Valley 
Schdy Airport 

Schdy Airport 

Schdy Airport 



SI seeding--Flight #129, 131 

SI seeding--Flight #130 
SI seeding 
SI seeding 
SI seeding 

SI seeding--Flight #132, 1338 

SI seeding--Flight #134 
Lapse-time movies 
Lapse-time movies 

SI seeding 

SI seeding 

SI seeding 

SI seeding--Flight #135 
SI seeding --Flight #135 
SI seeding --Flight #136 
SI seeding 

SI seeding 

SI seeding 

SI seeding 

SI seeding 

SI seeding 

SI seeding 

SI seeding--Flight #138 
SI seeding 

SI seeding 

SI seeding 

SI seeding 

Lapse-time movies 

SI seeding 

SI seeding 

Still photos; Flight #140, 141 

SI seeding 
SI seeding 
SI seeding 

SI seeding--F light unnumbered 

SI seeding 
SI seeding 
SI seeding 
SI seeding 
SI seeding 
Lapse-time movies 

Lapse-time movies; Flight #154 

Still photos 


Bibliography of Reference Literature 

Dunean Blanchard 

(1) ‘‘Observations on the Behavior of Water Drops at Terminal Velocity 
in Air’’; Project Cirrus Occasional Report #7 (November 1, 1948). 

(2) ‘‘The Distribution of Raindrops in Natural Rain’’; Project Cirrus 
Occasional Report #15 (November 15, 1949). 

(3)  ‘‘The Use of Sooted Screens for Determining Raindrop Size and 
Distribution’’; Project Cirrus Occasional Report #16 (November 
15, 1949). 

(4)  ‘‘Experiments with Water Drops and the Interaction Between Them 

at Terminal Velocity in Air’’; Project Cirrus Occasional Report #17 
(December 15, 1949). 

B. M. Cwilong 

(5) ‘‘Sublimatim in a Wilson Chamber’’; Nature, Vol. 155, p. 361 (1945). 

Raymond E. Falconer 

(6) ‘fA Method for Obtaining a Continuous Record of the Type of Clouds 
in the Sky During the Day’’; Project Cirrus Occasional Report #8 
(March 1, 1949). 

(7) ‘Some Correlations Between Variations in the Atmospheric Po- 
tential Gradient at Schenectady and Certain Meteorological Phe- 
nomena’’; Project Cirrus Occasional Report #18 (December 1, 1949). 

LTJG W..E. Hubert and H. J. Wells, AGC, U.S. Navy 

(8)  ‘‘Periodic Fluctuations in the Ohio Basin Moisture Balance’’, Pro- 
ject Cirrus Occasional Report #26 (January 15, 1951). 

(9)  ‘Seven-day Periodicity in Upper-air Temperatures Induced by 
Localized Silver -iodide Seeding’’; Project Cirrus Occasional Re- 
port #27 (January 15, 1951). 

(10) ‘Concentration of Ice-crystal Nuclei Under Various Weather 
Conditions’’; Project Cirrus Occasional Report #28 (June 15, 1951). 


Appendix IV 

Irving Langmuir 


‘Supercooled Water Droplets in Rising Currents of Cold Saturated Air’’; 
Research Laboratory Report No. RL-223 (October 1943-August 1944). 

(11A) ‘‘Memorandum on Introduction of Ice Nuclei Into Clouds’’; never pub- 








lished but available in Research Laboratory Library (August 16, 1946). 

“The Growth of Particles in Smokes and Clouds and the Production of 
Snow from Supercooled Clouds’’; Proc.Amer.Phil.Soc., Vol.92, p.167 
(July 1948). 

*‘The Production of Rain by a Chain Reaction in Cumulus Clouds at Tem- 
peratures Above Freezing’’; Jour.Met., Vol.5, p.175 (October 1948). 

‘Studies of the Effects Produced by Dry-Ice Seeding of Stratus Clouds’’; 
Project Cirrus Occasional Report #10 (December 31, 1948). 

“‘Larger-scale Seeding of Stratus and Cumulus Clouds with Dry Ice’’; 
Abstract of Am.Met.Soc. paper (January 25, 1949). 

“Outline of Progress in the Evaluation of Cloud Modification Techni- 
ques’’; Memorandum for Office Use (early 1950). 

Miscellaneous Letters and Reports (‘‘Seven-day Periodicity in the 
Weather During 1950’’; ‘‘Study of Periodicity in Rainfall Due to Silver- 
iodide Seeding in New Mexico’’; ‘‘Supplementary Remarks in Relation to 
the Tables and Figures’’); Folder prepared for Office Use (1950). 

*‘Progress in Cloud Modification by Project Cirrus’’; Project Cirrus 
Occasional Report #21 (April 15, 1950). 

““A Gamma Pattern Seeding of Stratus Clouds, Flight 52, and a Racetrack 
Pattern Seeding of Stratus Clouds, Flight 53’’; (with C.A. Woodman) 
Project Cirrus Occasional Report #23 (June 1, 1950). 

‘‘Results of the Seeding of Cumulus Clouds in New Mexico’’; Project 
Cirrus Occasional Report #24 (June 1, 1950). 

‘Studies of Tropical Clouds’’; Project Cirrus Occasional Report #25 
(July 1, 1950). 

‘‘Control of Precipitation from Cumulus Clouds by Various Seeding Tech- 
niques’’; Science, Vol.112, p.35 (July 14, 1950-Res. Lab. reprint-1730). 

‘‘Cause and Effect Versus Probability in Shower Production’’; Project 
Cirrus Occasional Report #22 (July 15, 1950). 


Appendix IV 

(24) ‘Cloud Seeding by Means of Dry Ice, Silver lodide, and Sodium 
Chloride’’; Trans.N.Y.Acad.Sci., Vol.14, p.40 (November 1951 - 
Res. Lab. reprint-1885). 

(25) ‘“‘A Seven-day Periodicity in Weather in the United States During 
April 1950’’; Bull.Amer.Met.Soc., Vol.31, p.386 (December 1950 - 
Res. Lab. reprint-1781). 

(26) ‘*‘Widespread Modifications of Synoptic Weather Conditions Induced 
by Localized Silver-iodide Seeding’’; Prepared in January 1951 and 
never published. 

L. B. Leopold and M, H. Halstead 

(26A) “‘First Trials of the Schaefer-Langmuir Dry-ice Cloud-seeding 
Technique in Hawaii’’; Bull. Amer.Met.Soc., Vol.29, No.10, p.525 
(December 1948). 

Vincent J. Schaefer 

(27) ‘*A method for Making Snowflake Replicas’’; Science, Vol.93, 
p.239 (March 1941). 

(28) ‘‘Making ‘Fossil’ Snowflakes’’; Schen.Mus.Topics, Vol.1, p.8 
(July 1941 - Res. Lab. reprint-1104). 

(29) ‘‘A Method of Making Replicas of Snowflakes, Ice Crystals, and 
Other Short-lived Substances’’; Mus.News, Vol.19, p.11 (Septem- 
ber 1941). 

(30) ‘‘Use of Snowflake Replicas for Studying Winter Storms’’; Nature, 
Vol.149, p.81 (January 17, 1942 - Res. Lab. reprint-1121). 

(31) ‘‘An Air Decelerator for Use on De-icing Precipitation Static and 
Weather Reconnaissance Planes’’; Report never published but avail- 
able in Schaefer’s office files (January 1945). 

(32) ‘“The Preparation and Use of Water-sensitive Coatings for Sampling 
Cloud Particles’’; Report never published but available in Schaefer’s 
office files (April 1946). 

(32A) ‘‘Final Report on Icing Research’’; available in Research Lab- 
oratory files (August 8, 1946). 


Appendix IV 

(33) ‘‘The Production of Ice Crystals in a Cloud of Supercooled Water Drop- < 
lets’’; Science, Vol.104, p.457 (November 15, 1946 - Res. Lab. reprint- 

(34) ‘‘Properties of Particles of Snow and the Electrical Effects They Pro- 
duce in Storms’’; Trans.AGU, Vol.28, p.587 (August 1947 - Res. Lab 

(35) ‘*‘Heat Requirements for Instruments and Airfoils During Icing Storms 
on Mt. Washington’’; Trans.ASME, Vol.69, p.843 (November 1947 - 
Res, Lab. reprint-1445). 

(36) ‘‘The Production of Clouds Containing Supercooled Water Droplets or 
Ice Crystals Under Laboratory Conditions’’; Bull.Amer.Met.Soc., Vol.29, 
p.175 (April 1948 - Res. Lab. reprint-1502). 

(37) ‘‘A New Plane Model Cloud Meter’’; (with R. E. Falconer), Project 
Cirrus Occasional Report #2 (May 15, 1948). 

(38) ‘The Natural and Artificial Formation of Snow in the Atmosphere’’; 
Trans.AGU, Vol.29, p.492 (August 1948 - Res. Lab. reprint-1532). 

(39) ‘*Types of Solid Precipitation in Snowstorms’’; Weatherwise, Vol.1, 
p.6 (December 1948 - Res. Lab. reprint-1582). 

(40) ‘‘Methods and Techniques for the Study of Atmospheric Nuclei, Clouds, 
and Precipitation’’; Abstract of Am.Met.Soc. paper (January 25, 1949). 

(41) ‘*‘The Detection of Ice Nuclei in the Free Atmosphere’’; Project Cirrus 
Occasional Report #9 (February 1, 1949). 

(42) ‘*The Possibility of Modifying Lightning Storms in the Northern Rockies’’; 
Project Cirrus Occasional Report #11 (February 1, 1949). 

(43) ‘*‘The Formation of Ice Crystals in the Laboratory and the Atmosphere’’; 
Chem.Rev., Vol.44, p.291 (April 1949 - Res. Lab. reprint-1601). 

(44) ‘‘Report on Cloud Studies in Puerto Rico’’; Project Cirrus Occasional 
Report #20 (January 15, 1950). 

(45) ‘*The Occurrence of Ice-crystal Nuclei in the Free Atmosphere’’; 
Project Cirrus Occasional Report #20 (January 15, 1950). 


Appendix IV 

(46) ‘‘A Confirmation of the Workman-Reynolds Effect’’; Phys.Rev., 
Vol.77, p.721 (March 1, 1950 - Res. Lab. reprint-1690). 

(47) “The Occurrence of Ice-crystal Nuclei in the Free Atmosphere”’; 
Proc.lst Nat.Air Pollution Symposium (March 1950 - Res. Lab. 

(48) ‘Induced Precipitation and Experimental Meteorology’’; Trans.NY Acad. 
S¢i., Vol.12, p.260 (June 1950 = Res. Lab. reprint-1745). 

(49) ‘“‘Experimental Meteorology’’; Journ.Appl.Math.&Phys., Vol.1, p.153 
(l950°=Res. Lab. reprint=1 706): 

(50) ‘“*The Effects Produced by Seeding Supercooled Clouds with Dry Ice 
and Silver Iodide’’; Cent.Proc.Roy.Met.Soc., p.42 (1950 - Res. Lab. 

(51) ‘“‘Effect of Sunlight on the Action of Silver-iodide Particles as Subli- 
mation Nuclei’’; (with B. Vonnegut, S. E. Reynolds, and W. Hume), Bull. 
Am.Met.Soc., Vol.32, p.47 (February 1951 - Res. Lab. reprint-1809). 

(52) “Snow and Its Relationship to Experimental Meteorology’’; Comp.of 
ee aViet ao 276 (Oat = Rest lab. reprint-le52)s 

(53) ‘‘A Cmtinious Cloud Chamber for Studying Small Particles in the 
Atmosphere’’; Project Cirrus Occasional Report #32 (March 1, 1952). 

(54) ‘‘The Formation of Ice Crystals in Ordinary and Nuclei-free Air”’; 
Project Cirrus Occasional Report #33 (March 1, 1952). 

(54A) ““The Concentration of Ice Nuclei at the Summit of Mt. Washington’’; 
Project Cirrus Occasional Report #35 (August 1, 1952). 

Robert Smith-Johannsen 

(55) ‘‘Some Experiments on the Freezing of Water’’; Project Cirrus 
Occasional Report #3 (June 1, 1948). 

Bernard Vonnegut 

(56) ‘‘The Nucleation of Ice Formation by Silver Iodide’’; Jour.Appl. 
Phys., Vol.18, p.593 (July 1947 - Res. Lab. reprint-1433). 


Appendix IV 

(57) ‘Nucleation of Ice Formation by Silver Iodide Particles’’; Supple- 
mentary to First Quarterly Progress Report, Project Cirrus (Nov- 
ember 15, 1947). 

(58) ‘Influence of Butyl Alcohol on Shape of Snow Crystals Formed in the 
Laboratory’’, Science, Vol.107, p.621 (June 11, 1948 - Res. Lab. 
reprint-1522); Project Cirrus Occasional Report #5. 

(59) ‘‘Smoke from Smelting Operations as a Possible Source of Silver- 
iodide Nuclei’’; (with R. E. Falconer), Project Cirrus Occasional 
Report #4 (June 15, 1948). 

(60) ‘‘Production of Ice Crystals by the Adiabatic Expansion of Gas’’; Pro- 
ject Cirrus Occasional Report #5 (September 15, 1948); Jour.Appl.Phys., 
Vol.19, p.959 (October 1948). 

(61) ‘Nucleation of Supercooled Water Clouds by Silver-iodide Smokes’’; 
Project Cirrus Occasional Report #5 (September 15, 1948); Chem.Rev., 
Vol.44, p.277 (April 1949). 

(62) ‘Variation with Temperature of the Nucleation Rate of Supercooled 
Liquid Tin and Water Drops’’; Project Cirrus Occasional Report #6 
(October 15, 1948); Jour.Coll.Sci., Vol.3, p.563 (December 1948 - 
Res. Lab. reprint-1567). 

(63) ‘‘A Capillary Collector for Measuring the Deposition of Water Drops 
on a Surface Moving Through Clouds’’; Rev.Sci.Instr., Vol.20, p.110 
(February 1949). 

(64) ‘‘Note on Nuclei for Ice Crystal Formation’’; Bull.Am.Met.Soc., Vol.30, 
p.194 (May 1949 - Res. Lah. reprint-1610). 

(65) ‘‘Silver-iodide S moke’’, Project Cirrus Occasional Report #13 
(July 1, 1949). 

(66) ‘‘Vortex Thermometer for Measuring True Air Temperatures and 
True Air Speeds in Flight’’; Project Cirrus Occasional Report #14 
(September 1, 1949); Rev.Sci.Instr.. 

(67) ‘*‘Continuous-recording Condensation Nuclei Meter’’; Project Cirrus 
Occasional Report #19 (January 1, 1950); Nat.Air Poll.Symp., 
Vol.1, p.36 (March 1950 - Res. Lab. reprint-1711). 

(68) ‘“Techniques for Generating Silver-iodide Smoke’’; Jour.Coll.Sci., 
Vol.5, p.37 (February 1950 - Res. Lab. reprint-1671). 

-101 - 

Appendix IV 

(69) ‘Experiments with Silver-iodide Smokes in the Natural Atmosphere’’; 
Bull.Am.Met.Soc., Vol.31, p.151 (May 1950 - Res. Lab. reprint-1724). 

(70) ‘‘Detection and Measurement of Aerosol Particles by the Use of an 
Electrically Heated Filament’’; (with R. E. Neubauer), Project Cir- 
rus Occasional Report #29 (September 1, 1951); Analytical Chemistry, 
Vol.24, p.1000 (June 1952). 

(71) ‘‘A Vortex Whistle’’; Project Cirrus Occasional Report #30 (Nov- 
ember 1, 1951). 

(72) ‘Recent Experiments on the Effect of Ultraviolet Light on Silver- 
iodide Nuclei’’; (with R. E. Neubauer), Bull.Am.Met.Soc., Vol.32, 
p.356 (November 1951 - Res. Lab. reprint-1894). 

(73) ‘‘Spray-nozzle Type of Silver-iodide Smoke Generator for Airplane 
Use’’; (with Kiah Maynard), Project Cirrus Occasional Report #31 
(February 15, 1952). 

(74) ‘‘Thin Films of Supersaturated Solutions for Detecting, Counting 
and Identifying Very Small Crystalline Particles’’; Project Cirrus 
Occasional Report #34 (April 15, 1952). 

(74A) ‘‘Counting Large Sodium-containing Particles in the Atmosphere 
by Their Spectral Emission in a Hydrogen Flame’’; (with Raymond 
‘L. Neubauer), Project Cirrus Occasional Report #38 (October 1, 1952). 

(74B) ‘‘Production of Monodisperse Liquid Particles by Electrical Atom- 
ization’’; (with Raymond L. Neubauer), Project Cirrus Occasional 
Report #36 (October 1, 1952). 

(74C) “‘Effect of Halogens on the Production of Condensation Nuclei by a 
Heated Platinum Wire’’; Project Cirrus Occasional Report #39 
(October 1, 1952). 

(74D) ‘‘Multiple-stage Dilution of Aerosols by Use of Aspirators’’; Pro- 
ject Cirrus Occasional Report #37 (October 1, 1952). 

-{748) “Ctoud Seeding’; Scientific Ameritean; Vork.186, pp17-21 (January 1952). 

(74F) ‘The Science of Rainmaki me Technion Yearbook, Volo p.82 
ng > 


Appendix IV 

Project Cirrus Reports 
(75) First Quarterly Progress Report, July 15, 1947. 
(76) Second Quarterly Progress Report, November 15, 1947. 
(77) Third Quarterly Progress Report, February 15, 1948. 
(78) Fourth Quarterly Progress Report, July 1, 1948. 
(79) Fifth Quarterly Progress Report, September 15, 1948. 
(80) Final Report, Contract W-36-039-SC -32427, December 31, 1948. 
(81) Sixth Quarterly Progress Report, January 28, 1949. 
(82) Seventh Quarterly Progress Report, March 15, 1949. 
(83) Eighth Quarterly Progress Report, June 15, 1949. 
(84) Ninth Quarterly Progress Report, September 15, 1949. 
(85) Tenth Quarterly Progress Report, December 30, 1949. 
(86) Eleventh Quarterly Progress Report, March 30, 1950. 
(87) Twelfth Quarterly Progress Report, July 30, 1950. 
(88) Thirteenth Quarterly Progress Report, October 30, 1950. 
(89) Fourteenth Quarterly Progress Report, January 30, 1951. 
(90) Fifteenth Quarterly Progress Report, April 30, 1951. 

(91) Final Report, Contract W-36-039-SC-38141, July 30, 1951. 

-103 - 

Appendix IV 
Bibliography - 


(92) ‘‘Report of Cloud-seeding Experiments in the San Diego County and 
the Santa Ana River Watershed’’; revised edition June 10, 1952, pub- 
lished by John A. Battle, consulting meteorologist, Beaumont, Cali- 

(93) ‘‘Weather Control and Augmented Potable Water Supply’’; Extracts 
from hearings before subcommittees of the committees on Interior 
and Insular Affairs; Interstate & Foreign Commerce; and Agriculture 
& Forestry; United States Senate, 82d Congress, First Sessions; on 
SeOwoeacc, ands. oon Washington. DL ©. March i4s 15.16. 19. and 
April 5, 1951; U.S. Government Printing Office. 


Additional copies of this report will be supplied 
to qualified persons upon application to: 

Research Publication Services 
Room 2E38, The Knolls 

R.J. Cordiner, New York H.A. Winne, Schenectady 
P.D. Reed, New York N.M. DuChemin, Schenectady 
H. V. Erben, Schenectady J.L. Busey, New York 
R.W. Johnson, New York D.L. Millham, Schenectady 

R, Paxton, New York L.R. Boulware, New York 
J.W. Belanger, Schenectady C.H. Lang, New York 
H.F. Smiddy, New York R.H. Luebbe, New York 

C.G. Suits, Schenectady 

I, Langmuir, Schenectady 
V.J. Schaefer, (12) Schenectady 
B, Vonnegut 
Arthur D. Little, Inc., Cambridge, Mass. 
R.E. Falconer, Schenectady 
K, Maynard, Schenectady 
R.L. Neubauer, Schenectady 
R. Smith-Johannsen, Waterford 
7, ©). Blanchard 
a Woods Hole Oceanographic Inst., Woods Hole, Mass. 
M. Geller 
Massachusetts Institute of Technology, Cambridge, Mass. 
Charles Woodman, Meter and Instrument Dept., West Lynn 
Arthur Parr, Schenectady 
George Blair, Malta 

Evans Signal Laboratory, Belmar, New Jersey 
Michael J. Ference, Jr. 
C.J. Brasefield 

Committee on Geophysical Sciences, Office of Naval Research, Wash. D.C. 
E.G, Droessler 
Commander R.A. Chandler 
Lieutenant Max A. Eaton 
Commander G.D. Good 

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Major P.J. Keating Colonel N.C. Spencer 
Lieutenant Colonel J. Tucker 

Office of Naval Operations, Washington 25, D.C. 

Commander Daniel F. Rex 

Electronics Squadron, Griffiss Air Force Base, Rome, New York 

Captain J.A. Plummer 

Squier Signal Laboratory, Ft. Monmouth, New Jersey 


Samuel Stine 
Colonel Rudolph C. Koerner, Jr. 

Eugene Bollay 
North American Weather Consultants, 1187 No. Green St., 
Pasadena, Calif. 
Dr. Irving P. Krick 
Water Resources Development Corp., 460S. Broadway, Denver, Colo. 
William Hartnett 
Weathercasts of America, 2123 Railway Exch. Building, St. Louis, Mo. 
Professor Carl G. Rossby 
Institute of Meteorology, 103 Flemingatan, University of Stockholm, 
Stockholm, Sweden 
Professor P.E. Sheppard 
Dept. of Meteorology, Imperial College, Exhibition Road, London, nee 
Professor R. Sanger 
Polytechnic Institute, Zurich, Switzerland 
Lieutenant (JG) W.E. Hubert 
Institute of Meteorology, University of Stockholm, Stockholm, Sweden 

. Hod Wells, AGC 

Project Scud, Com. Air. Lant., Atlantic Fleet Weather Control, 
Norfolk, Va. 
Commander C.E. Tilden 
Project Scud, Com. Air. Lant., Atlantic Fleet Weather Control, 
Norfolk, Va. 
Joseph Silverthorne 
c/o Empressa Dean, Tegucigalpa, Honduras 
Maurice Halstead 
c/o Johns Hopkins Climatological Laboratory, Seabrook, New Jersey 
Joseph B. Dodge 
Gorham, New Hampshire 
Alan Bemis 
Massachusetts Institute of Technology, Cambridge, Mass. 
Millikin & Farwell, Inc. 
1002 Whitney Building, New Orleans, La. 
Wallace E. Howell Associates 
Cambridge, Mass. 
Jack Barrows 
Chief, Fire Research Region I, U.S. Forest Service, Missould, Mont. 
Dr, Marcel de Quervain 
Institute for Study of Snow and Avalanches 
Davosdorf/Weissfluhjoch, Switzerland 

OTHER (continued) 
Signal Corps Engineering Laboratories, Fort Monmouth, N.J. 
General E.R. Petzing 
Dre A Zaki 
Dr. M. Ference 
S.E. Petrillo 
E.L. Nelson 
Bd. Fister 

Office of the Chief Signal Officer, Washington 25, D.C. 
Major General G. 1. Back 

Brigadier General J. D. O’Connell 

Colonel C.J. King 

Nela Park Library, Cleveland 
Electronics Park Library, Syracuse 
Main Library, Schenectady 
William Stanley Library, Pittsfield 
Thomson Laboratory Library, River Works 
F.E. Arnold, West Lynn Library 
Chemical Division Library, Pittsfield 
Aircraft Gas Turbine Library, Lockland, Ohio 
Household Refrig. Library, Erie 
Switchgear Department Library, Philadelphia 
Loco. and Car Equip. Dept. Library, Erie 
Fort Wayne Library 
KAPL Library 
Johnson City Library 
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Research Laboratory Library, The Knolls 
Accessory Turbine Library, 63NG, River Works 



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ae, Melanie iC, Rives 
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ie Ae RIC Hh ET ET 

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Patent Services Department, Schenectady 
PA. Frank 

Research Laboratory, The Knolls, Schenectady 
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RW; Larson 
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Mood “Ozerott 
EM. Pell 
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NOs Or: 




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Attn: Code N428 

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Attn: Director of R&D, DCS/M 

Director, Mt. Washington Observatory 
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U.S. Weather Bureau, 24th and M Streets, N.W., Washington 25, D.C, 
Attn: Dr. H. Wexler 

U.S. Weather Bureau, 24th and M Streets, N.W., Washington 25, D.C. 
tins Digsnoss Gunn 

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No. of 

N.A.C.A. Laboratories, Cleveland Airport, Cleveland, Ohio 
Attny Mx, L.A, Rodert 
1 Massachusetts Institute of Technology, Department 6f Meteorology, 

Cambridge 39, Massachusetts, Attn: Dr. H.G. Houghton 

1 New York University, Department of Meteorology, New York, New York 
Attn: Dr. B. Haur witz 

1 University of Minnesota, Institute of Technology, Minneapolis 14, Minn. 
Attn: Athelstan F. Spilhaus, Dean 

1 University of Chicago, Department of Meteorology, Chicago, Illinois 
Attn: Dr, Horace Byers 

il University of California at Los Angeles, Department of Meteorology, 
Los Angeles, California, Attn: Dr. M. Neiburger 

iL Pennsylvania State College, Division of Meteorology, State College, 
Pennsylvania, Attn: Mr. H. Neuberger 

if Director, Blue Hill Observatory, Milton 86, Massachusetts 

i Institute for Advanced Study, Princeton, New Jersey 
Attn: Dr. J. Von Neumann 


cl Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 
Ating sor. @7). Iselin 

1 St. Louis University, 3621 Olive Street, St. Louis 8, Missouri 
Attn: Dr. J. B. Macelwane, S.J. 

it Electrical Engineering Res. Lab., The University of Texas, Box F, 
University Station, Austin 12, Texas 

1 New Mexico School of Mines, Box 6000, Station A Seas ae 
New Mexico, Attn: Dr. E.J. Workman 

1 University of New Mexico, Albuquerque, New Mexico, Attn: Dr. V.H. Regen 
i Scripps Institute of Oceanography, La Jolla, California, Attn: D. Leipper 

il Cornell Aeronautical Laboratory, P.O. Box 235, Buffalo 21, New York 
Attn: Dr: S. Chapman 

No. of 




Chief, State Water Survey Division, Urbana, Illinois 

Chairman, Operations Committee, PROJECT CIRRUS, General 
Electric Hangar, Schenectady County Airport, Schenectady 

Mr. Louis W. Jolliff, 1108 West Columbia, Champaign, Illinois 

Professor Thompson, Meteorological Head Office, 315 Bloor Street 
West Toronto, Ontario 

Mr, E.L. Davies, Deputy Chairman, Defense Research Board, 
Ottawa, Ontario 

Mr. G.W.C. Tait, Suffield Experimental Station, Suffield, Alberta 

New York University, College of Engineering, University Heights, 
New York 53, New York, Attn: Dr. H.K. Work, Director of Research 

U.S. Department of Agriculture, Division of Fire Research, 
Washington 25, D.C., Attn: A;A. Brown, Chief 

University of Alaska, College, Alaska, Attn: Dr. E.F. George 
Commercial Service Section, Syracuse, New York, Attn: C.P. Reynolds 
Armed Forces College, Norfolk 11, Virginia 

Chemical Corps Technical Command, Army Chemical Center, 
Maryland, Attn: Dr. Solomon Love 

Mr. H.F. Huddleston, U.S. Department of Agriculture, Bureau of 
Agriculture Economics, Division of Agriculture Estimates, 
Washington, D.C. 

American Meteorological Society, Boston 8, Massachusetts 

Bureau of Aeronautics, Project AROWA, Norfolk, Virginia 

Mp 4s 




Kescarch Laboe